soc/amd/common/block/psp/psb: add missing amdblocks/smn.h include

smn_read32 is used in this file, so include the header file with the
function prototype so that the file compiles successfully.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I5bef96cd08f22b3475e8b5ba4e984a6e1ab4da36
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66913
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Matt DeVillier <matt.devillier@amd.corp-partner.google.com>

src/soc/amd/common/block/psp/psb.c

@@ -3,6 +3,7 @@
 #include <arch/mmio.h>
 #include <bootstate.h>
 #include <amdblocks/reset.h>
+#include <amdblocks/smn.h>
 #include <console/console.h>
 #include <cpu/amd/msr.h>
 #include <types.h>