ghes: move structures/enum to a header file

As a ghes_edac driver will need to access ghes structures, in order
to properly handle the errors, move those structures to a separate
header file. No functional changes.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

diff --cc drivers/acpi/apei/ghes.c
Simple merge

diff --cc include/acpi/ghes.h
Simple merge