drivers/smmstore: Expose region device

Allow other drivers to use the SMMSTORE region device.

Change-Id: I6316b703829590bd6f41c3d4013b4a4660b9cbab
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/62014
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>

src/include/smmstore.h

@@ -115,6 +115,8 @@ int smmstore_rawclear_region(uint32_t block_id);
 #if ENV_RAMSTAGE
 int smmstore_get_info(struct smmstore_params_info *info);
 #endif
+struct region_device;
+int smmstore_lookup_region(struct region_device *rstore);
 
 /* Advertise SMMSTORE v2 support */
 struct lb_header;