cpu/x86/smm: Add qemu's SMM-Revision Level

The SMI handler on qemu returned early, due to missing SMM-Revision
Level support.

Add the ID qemu uses, which is AMD64 compatible for qemu-system-x86_64.

Fixes booting tianocore payload with SMM variable store on qemu.

Change-Id: I978b94150cfc49a39c2a0818eb14a649850e451d
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/c/31594
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/cpu/x86/smm/smihandler.c

@@ -168,6 +168,7 @@ void smi_handler(u32 smm_revision)
 			smm_save_state(smm_base,
 				       SMM_EM64T101_ARCH_OFFSET, node);
 		break;
+	case 0x00020064:
 	case 0x00030064:
 		state_save.type = AMD64;
 		state_save.amd64_state_save =