EFI: add efi_arch_cfg_file_early/late() to handle arch specific cfg file fields

EFI: add efi_arch_cfg_file_early/late() to handle arch specific cfg file fields

Different architectures have some different configuration file
fields that need to be handled.  In particular, x86 has ucode
and ARM has device tree files to be loaded.  These arch specific
functions is used to allow each architecture to implement these
features in arch specific code.  Early/late versions are provided,
as ARM needs to process the DTB entry first, and x86 wants to process
the ucode entry last as it is the smallest allocation.

Signed-off-by: Roy Franz <roy.franz@linaro.org>
Acked-by: Jan Beulich <jbeulich@suse.com>