Add smm_variable service provider

Adds an implementation of a service provider for the smm_variable
service. Accepts uefi variable requests and uses the
uefi_variable_store as the backend for storage.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: I050fc26c03b4d0098ccc303a293b8faeab488419
4 files changed