cpu/x86/smm: Promote smm_subregion()

No need to limit these declarations to FSP. Both
PARALLEL_MP_INIT smm_relocate() and TSEG_STAGE_CACHE
can be built on top of this.

Change-Id: I7b0b9b8c8bee03aabe251c50c47dc42f6596e169
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34701
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>

src/soc/intel/apollolake/cpu.c

@@ -29,10 +29,10 @@
 #include <cpu/intel/turbo.h>
 #include <cpu/x86/msr.h>
 #include <cpu/x86/mtrr.h>
+#include <cpu/x86/smm.h>
 #include <device/device.h>
 #include <device/pci.h>
 #include <fsp/api.h>
-#include <fsp/memmap.h>
 #include <intelblocks/cpulib.h>
 #include <intelblocks/fast_spi.h>
 #include <intelblocks/mp_init.h>