Make sure to always fall back to xen_early_console, even for dom0

Move the pvh_xencons so xen_machdep.c as early_xencons, so it can be
used in the future as early ouput for plain PV guests too.

xen: declare 'default_consinfo' as extern in a header

this makes pvh_consinit.c actually compile with CONS_OVERRIDE set.
i didn't see any good header to add to (bootinfo.h and cpu.h both
seem to be poor choices but were considered), hence the new one
with just this definition.

Allow a PVH dom0 to use VGA as console: make xen_pvh_consinit() return 1 if
it handles the console and 0 otherwise (especially when console=tty0 or
console=pc is present on the command line).
In consinit() fallback to native console selection if xen_pvh_consinit()
returns 0.

branches: 1.2.20;
Hanble dom0 console. This one doesn't need a ring to be mapped, and
can be used earlier.

Introduce Xen PVH support in GENERIC.
This is compiled in with
options XENPVHVM
x86 changes:
- add Xen section and xen pvh entry points to locore.S. Set vm_guest
to VM_GUEST_XENPVH in this entry point.
Most of the boot procedure (especially page table setup and switch to
paged mode) is shared with native.
- change some x86_delay() to delay_func(), which points to x86_delay() for
native/HVM, and xen_delay() for PVH

Xen changes:
- remove Xen bits from init_x86_64_ksyms() and init386_ksyms()
and move to xen_init_ksyms(), used for both PV and PVH
- set ISA no-legacy-devices property for PVH
- factor out code from Xen's cpu_bootconf() to xen_bootconf()
in xen_machdep.c
- set up a specific pvh_consinit() which starts with printk()
(which uses a simple hypercall that is available early) and switch to
xencons when we can use pmap_kenter_pa().

xen: declare 'default_consinfo' as extern in a header

this makes pvh_consinit.c actually compile with CONS_OVERRIDE set.
i didn't see any good header to add to (bootinfo.h and cpu.h both
seem to be poor choices but were considered), hence the new one
with just this definition.

Allow a PVH dom0 to use VGA as console: make xen_pvh_consinit() return 1 if
it handles the console and 0 otherwise (especially when console=tty0 or
console=pc is present on the command line).
In consinit() fallback to native console selection if xen_pvh_consinit()
returns 0.

branches: 1.2.20;
Hanble dom0 console. This one doesn't need a ring to be mapped, and
can be used earlier.

Introduce Xen PVH support in GENERIC.
This is compiled in with
options XENPVHVM
x86 changes:
- add Xen section and xen pvh entry points to locore.S. Set vm_guest
to VM_GUEST_XENPVH in this entry point.
Most of the boot procedure (especially page table setup and switch to
paged mode) is shared with native.
- change some x86_delay() to delay_func(), which points to x86_delay() for
native/HVM, and xen_delay() for PVH

Xen changes:
- remove Xen bits from init_x86_64_ksyms() and init386_ksyms()
and move to xen_init_ksyms(), used for both PV and PVH
- set ISA no-legacy-devices property for PVH
- factor out code from Xen's cpu_bootconf() to xen_bootconf()
in xen_machdep.c
- set up a specific pvh_consinit() which starts with printk()
(which uses a simple hypercall that is available early) and switch to
xencons when we can use pmap_kenter_pa().

Allow a PVH dom0 to use VGA as console: make xen_pvh_consinit() return 1 if
it handles the console and 0 otherwise (especially when console=tty0 or
console=pc is present on the command line).
In consinit() fallback to native console selection if xen_pvh_consinit()
returns 0.

branches: 1.2.20;
Hanble dom0 console. This one doesn't need a ring to be mapped, and
can be used earlier.

Introduce Xen PVH support in GENERIC.
This is compiled in with
options XENPVHVM
x86 changes:
- add Xen section and xen pvh entry points to locore.S. Set vm_guest
to VM_GUEST_XENPVH in this entry point.
Most of the boot procedure (especially page table setup and switch to
paged mode) is shared with native.
- change some x86_delay() to delay_func(), which points to x86_delay() for
native/HVM, and xen_delay() for PVH

Xen changes:
- remove Xen bits from init_x86_64_ksyms() and init386_ksyms()
and move to xen_init_ksyms(), used for both PV and PVH
- set ISA no-legacy-devices property for PVH
- factor out code from Xen's cpu_bootconf() to xen_bootconf()
in xen_machdep.c
- set up a specific pvh_consinit() which starts with printk()
(which uses a simple hypercall that is available early) and switch to
xencons when we can use pmap_kenter_pa().

Hanble dom0 console. This one doesn't need a ring to be mapped, and
can be used earlier.

Introduce Xen PVH support in GENERIC.
This is compiled in with
options XENPVHVM
x86 changes:
- add Xen section and xen pvh entry points to locore.S. Set vm_guest
to VM_GUEST_XENPVH in this entry point.
Most of the boot procedure (especially page table setup and switch to
paged mode) is shared with native.
- change some x86_delay() to delay_func(), which points to x86_delay() for
native/HVM, and xen_delay() for PVH

Xen changes:
- remove Xen bits from init_x86_64_ksyms() and init386_ksyms()
and move to xen_init_ksyms(), used for both PV and PVH
- set ISA no-legacy-devices property for PVH
- factor out code from Xen's cpu_bootconf() to xen_bootconf()
in xen_machdep.c
- set up a specific pvh_consinit() which starts with printk()
(which uses a simple hypercall that is available early) and switch to
xencons when we can use pmap_kenter_pa().