soc/intel/common/block/smm: Add mainboard_smi_finalize

This commit adds a method called `mainboard_smi_finalize` which provides
a mechanism for a mainboard to execute some code as part of the finalize
method in the SMM stage before SoC does its finalization.

BUG=b:191189275
BRANCH=None
TEST=Implement `mainboard_smi_finalize` on lalala and verify that the
code executes in SMM.

Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Change-Id: If1ee63431e3c2a5831a4656c3a361229acff3f42
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55649
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>

src/cpu/x86/smm/smihandler.c

@@ -208,3 +208,4 @@ void __weak southbridge_smi_handler(void) {}
 void __weak mainboard_smi_gpi(u32 gpi_sts) {}
 int __weak mainboard_smi_apmc(u8 data) { return 0; }
 void __weak mainboard_smi_sleep(u8 slp_typ) {}
+void __weak mainboard_smi_finalize(void) {}

src/cpu/x86/smm/smm_module_handler.c

@@ -198,3 +198,4 @@ void __weak southbridge_smi_handler() {}
 void __weak mainboard_smi_gpi(u32 gpi_sts) {}
 int __weak mainboard_smi_apmc(u8 data) { return 0; }
 void __weak mainboard_smi_sleep(u8 slp_typ) {}
+void __weak mainboard_smi_finalize(void) {}