SMP: Introduce ENABLE_SMP_SUPPORT

- Make it more readable and less confusing compared to the 'CONFIG_MAX_NUM_NODES > 1' check

SELFOUR-501: x86 - Remove PAE support

x86: Remove duplication of the multiboot header

x86: Explicitly define kernel stack size

This commit changes the previous hard coded 4K kernel stack size
to being a configurable power of 2 sized stack

x86: Add BSS regions for BOOT and PHYS code

Uninitialized data structures in BOOT and PHYS code currently get
placed in sections that are allocated in the file of the final image.
Whilst these sections will get reclaimed during kernel boot, so no
runtime memory is being wasted, it results in kernel images that
are much larger to load and transport than necesary.

This change adds explicit BSS regions for both BOOT and PHYS code
and moves all appropriate data structures into them

Update SMP idle thread handling

SELFOUR-630:preliminary booting application processors
- update core detection code and Kconfig file
- update kernel stack managment so that BSP does not use boot stack before IPI APs
- move arch dependant data to a single structure
- add cache line size to Kconfig
- add cpu indexing and apic id mapping
- boot APs to halting state
- add guard for kernel stack if there is only one core

Revert "Merge pull request #358 in SEL4/sel4 from ~AZARRABI/sel4:multicore to master"

This reverts commit ce2f666bb811c5e4c779829fcb09d5a189ebcdbb, reversing
changes made to dc183f96b81f2344d7d0d910fc430f924eaae940.

SELFOUR-630:preliminary booting application processors
- update core detection code and Kconfig file
- update kernel stack managment so that BSP does not use boot stack before IPI APs
- move arch dependant data to a single structure
- add cache line size to Kconfig
- add cpu indexing and apic id mapping
- boot APs to halting state
- add guard for kernel stack if there is only one core

x86: Remove underscores from symbols as they are in violation of the C standard

x86: Define a KERNEL_BASE_OFFSET for translating the kernel image region

This definition is different to BASE_OFFSET in that it is only meant to
apply to the kernel image portion of the kernel window, and doesn't
assume that the entire window can be translated by a single offset

x86: Move APIC frequency calculation to APIC init, instead of doing it before we initialize paging

x86: Move 32-bit specific files into 'mode' directories, and only build if IA32