feat(fvp): enable kernel dt convention

Enable USE_KERNEL_DT_CONVENTION for the FVP platform to pass the DT blob
(DTB) in x0 to BL33. This aligns with the Linux boot protocol as
described in Documentation/arm64/booting.rst.

In addition:

- Clean up legacy ARM_LINUX_KERNEL_AS_BL33 handling since
  USE_KERNEL_DT_CONVENTION now implies this mode for DT handoff.
- Override args.arg0 for BL33 to point to ARM_PRELOADED_DTB_BASE in
  RESET_TO_BL31.
- Skip setting the primary MPID in x0 when using this convention.

Change-Id: Ieea8cfe68104b82038b9311613abf13afe7b48f1
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
4 files changed