UPSTREAM: of/fdt: factor out assignment of initrd_start/initrd_end

UPSTREAM: of/fdt: factor out assignment of initrd_start/initrd_end

Since architectures may not yet have their linear mapping up and running
when the initrd address is discovered from the DT, factor out the
assignment of initrd_start and initrd_end, so that an architecture can
override it and use the translation it needs.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Bug: 30369029
Patchset: kaslr-arm64-4.4

(cherry picked from commit 369bc9abf22bf026e8645a4dd746b90649a2f6ee)
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Change-Id: I8c258bdc4367955314e9a5223dc4c7751a06a98d