soc/amd/common: Add initial support for AMD PSP

Add files for supporting the BIOS->PSP communication not
covered by AGESA. The first command implemented notifies the
PSP that DRAM is ready.

This patch also introduces the amd/common/block directory
structure similar to intel/common/block.

Change-Id: I34b2744b071aa3dfb1071b2aabde32ddb662ab87
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/19753
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>
9 files changed