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>

src/soc/amd/stoneyridge/Kconfig

@@ -40,8 +40,10 @@ config CPU_SPECIFIC_OPTIONS
 	select TSC_CONSTANT_RATE
 	select SPI_FLASH if HAVE_ACPI_RESUME
 	select TSC_SYNC_LFENCE
-	select SOC_AMD_COMMON
 	select SOC_AMD_PI
+	select SOC_AMD_COMMON
+	select SOC_AMD_COMMON_BLOCK
+	select SOC_AMD_COMMON_BLOCK_PSP
 
 config UDELAY_LAPIC_FIXED_FSB
 	int