ARM/u-boot: Add support for FDTs passed in the uImage

Since we're using multi-part uImage format, we can add the FDT as
a seperate "blob" in the uImage, if the used U-Boot version is not
"FDT enabled".

This is used for example for our Verdex target. Currently I've got
a local hack in the platform/u-boot/Jamfile, looking into pulling
in the FDT files and a proper Jam setup to do that properly...

U-Boot: check for /chosen in the FDT for an initrd holding our tgz

* since the FDT linux boot method doesn't pass the uimage, we can't
use it to pass the kernel+driver tgz in a multi-file uimage.
* instead we check for the linux initrd properties in the /chosen node.

(cherry picked from my sam460ex branch)

U-Boot: initialize the debug UART using FDT hints when possible

* we first try to find 'serial', 'serial0' or 'serial1' in /aliases
* extract the required properties from the found node and use them
* fallback to the hardcoded UART from the board definition header

(cherry picked from my sam460ex branch)

U-Boot: dump the passed FDT

* add some helpers for Flattened Device Trees, for now a dump call
* dump the passed FDT on startup for now

Conflicts:
src/system/boot/platform/u-boot/Jamfile

(cherry picked from my sam460ex branch)

Fixes for other platforms.

Support static_cast on FixedWidthPointer.

Added an ELF64 version of preloaded_image.

* There is now 2 structures, preloaded_elf32_image and preloaded_elf64_image,
which both inherit from preloaded_image.
* For now I've just hardcoded in use of preloaded_elf32_image, but the
bootloader ELF code will shortly be converted to use templates which use
the appropriate structure. The kernel will be changed later when I add
ELF64 support to it.
* All kernel_args data is now compatible between 32-bit and 64-bit kernels.

U-Boot: move gFDT declaration to shell.S

* this avoids it falling into the BSS section which we clear quite late,
and allows setting it from asm code if needed.

U-Boot: save passed FDT and call common code

* should work better this way :D

Cleanup U-Boot global data struct

* there are only a few members we can really rely on, the rest is compile-time dependant.
* don't use ARM-specific stuff.

Drop ARM-specific register pointer

* the global data is already stored in a variable from shell.S anyway when available

Add empty C linux-style entry points

* On PPC, there are two different kernel entry signatures for Linux

Rename u-boot start2.cpp to start.cpp

* rename the file for consistency with other platforms.
* there used to be a start.S, long since renamed to shell.S anyway.

ARM/u-boot: Add support for FDTs passed in the uImage

Since we're using multi-part uImage format, we can add the FDT as
a seperate "blob" in the uImage, if the used U-Boot version is not
"FDT enabled".

This is used for example for our Verdex target. Currently I've got
a local hack in the platform/u-boot/Jamfile, looking into pulling
in the FDT files and a proper Jam setup to do that properly...

U-Boot: check for /chosen in the FDT for an initrd holding our tgz

* since the FDT linux boot method doesn't pass the uimage, we can't
use it to pass the kernel+driver tgz in a multi-file uimage.
* instead we check for the linux initrd properties in the /chosen node.

(cherry picked from my sam460ex branch)

U-Boot: initialize the debug UART using FDT hints when possible

* we first try to find 'serial', 'serial0' or 'serial1' in /aliases
* extract the required properties from the found node and use them
* fallback to the hardcoded UART from the board definition header

(cherry picked from my sam460ex branch)

U-Boot: dump the passed FDT

* add some helpers for Flattened Device Trees, for now a dump call
* dump the passed FDT on startup for now

Conflicts:
src/system/boot/platform/u-boot/Jamfile

(cherry picked from my sam460ex branch)

Fixes for other platforms.

Support static_cast on FixedWidthPointer.

Added an ELF64 version of preloaded_image.

* There is now 2 structures, preloaded_elf32_image and preloaded_elf64_image,
which both inherit from preloaded_image.
* For now I've just hardcoded in use of preloaded_elf32_image, but the
bootloader ELF code will shortly be converted to use templates which use
the appropriate structure. The kernel will be changed later when I add
ELF64 support to it.
* All kernel_args data is now compatible between 32-bit and 64-bit kernels.

U-Boot: move gFDT declaration to shell.S

* this avoids it falling into the BSS section which we clear quite late,
and allows setting it from asm code if needed.

U-Boot: save passed FDT and call common code

* should work better this way :D

Cleanup U-Boot global data struct

* there are only a few members we can really rely on, the rest is compile-time dependant.
* don't use ARM-specific stuff.

Drop ARM-specific register pointer

* the global data is already stored in a variable from shell.S anyway when available

Add empty C linux-style entry points

* On PPC, there are two different kernel entry signatures for Linux

Rename u-boot start2.cpp to start.cpp

* rename the file for consistency with other platforms.
* there used to be a start.S, long since renamed to shell.S anyway.