efi-stub.txt updates for ARM

Update efi-stub.txt documentation to be more general
and not x86 specific.  Add ARM only "dtb=" command
line option description.

Signed-off-by: Roy Franz <roy.franz@linaro.org>
Add shared update_fdt() function for ARM/ARM64

Both ARM and ARM64 stubs will update the device tree
that they pass to the kernel.  In both cases they
primarily need to add the same UEFI related information,
so the function can be shared.
Create a new FDT related file for this to avoid use
of architecture #ifdefs in efi-stub-helper.c
Change EFI allocation type for memory map to
EFI_RUNTIME_SERVICES_DATA, since we are passing
this buffer to the kernel, or immediately freeing it.

Signed-off-by: Roy Franz <roy.franz@linaro.org>
arm64: add EFI stub

This patch adds PE/COFF header fields to the start of the Image
so that it appears as an EFI application to EFI firmware. An EFI
stub is included to allow direct booting of the kernel Image. Due
to EFI firmware limitations, only little endian kernels with 4K
page sizes are supported at this time. Support in the COFF header
for signed images was provided by Ard Biesheuvel.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
doc: arm64: add description of EFI stub support

Signed-off-by: Mark Salter <msalter@redhat.com>
arm64: add EFI runtime services

This patch adds EFI runtime support for arm64. The runtime support allows the
kernel to access various EFI runtime services provided by EFI firmware. Things
like reboot, real time clock, EFI boot variables, and others.

Signed-off-by: Mark Salter <msalter@redhat.com>
arm64: efi stub cmdline hack. NOT FOR UPSTREAM