soc/amd/picasso: Add common PSP support

Add a new psp.c file so the base address can be determined, and select
the common/block/psp feature.

BUG=b:153677737

Change-Id: I322fd11a867a817375ff38a008219f9236c4f2ea
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://chromium-review.googlesource.com/2020368
Tested-by: Eric Peers <epeers@google.com>
Reviewed-by: Eric Peers <epeers@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40296
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/picasso/psp.c

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* This file is part of the coreboot project. */
+
+#include <console/console.h>
+#include <cpu/x86/msr.h>
+#include <amdblocks/psp.h>
+
+#define PSP_MAILBOX_OFFSET		0x10570
+#define MSR_CU_CBBCFG			0xc00110a2
+
+void *soc_get_mbox_address(void)
+{
+	uintptr_t psp_mmio;
+
+	psp_mmio = rdmsr(MSR_CU_CBBCFG).lo;
+	if (psp_mmio == 0xffffffff) {
+		printk(BIOS_WARNING, "PSP: MSR_CU_CBBCFG uninitialized\n");
+		return 0;
+	}
+
+	return (void *)(psp_mmio + PSP_MAILBOX_OFFSET);
+}