Add smm-variable service level tests

Adds tests that use the public service access protocol to verify
client access to the smm-variable service. A C++ client is added
to facilitate testing. Service level tests may be run in a native
PC environment or from Linux user-space on a real target.

Signed-off-by: Julian Hall <julian.hall@arm.com>
Change-Id: I6f2ecdcb3517b1392d689b41eeb17bda7e58952c
6 files changed