FROMLIST: of: fdt: allow to register arch specific hook validating reserved region

Add a possibility to register arch specific hook which will validate if
reserved-memory region passed by DT is valid (e.g. in case of x86, which
allows to boot with both ACPI and DT at the same time, registered hook
will validate if reserved-memory region passed by DT is covered by E820
reserved region entry).

Signed-off-by: Grzegorz Jaszczyk <jaszczyk@google.com>

Bug: 399581144
Link: https://lore.kernel.org/all/20250418124718.1009563-2-jaszczyk@chromium.org/


Change-Id: I242090842703d6be703c032992f0af8cdecae64c
Signed-off-by: Grzegorz Jaszczyk <jaszczyk@google.com>