mb/intel/mtlrvp: Add MTL-P RVP board ids

This adds MTL-P board id definition. Change include,
1. Add board_id.c implementation
2. Add board_id.h implementation
3. Add board_id config in variants.h
4. Makefile changes

BUG=b:224325352
TEST=Able to build with the patch and boot the mtlrvp platform with the
subsequent patches in the train

Signed-off-by: Jamie Ryu <jamie.m.ryu@intel.com>
Change-Id: I90b0543d5db208f696d2c2c2dc3d2581514a845b
Signed-off-by: Harsha B R <harsha.b.r@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66102
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Usha P <usha.p@intel.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>

src/mainboard/intel/mtlrvp/Makefile.inc

@@ -6,4 +6,5 @@ BASEBOARD_DIR:=$(call strip_quotes,$(CONFIG_BASEBOARD_DIR))
 subdirs-y += variants/baseboard/$(BASEBOARD_DIR)
 subdirs-y += variants/$(VARIANT_DIR)
 
+CPPFLAGS_common += -I$(src)/mainboard/$(MAINBOARDDIR)/variants/baseboard/include
 CPPFLAGS_common += -I$(src)/mainboard/$(MAINBOARDDIR)/variants/baseboard/$(BASEBOARD_DIR)/include

src/mainboard/intel/mtlrvp/variants/baseboard/include/baseboard/variants.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __BASEBOARD_VARIANTS_H__
+#define __BASEBOARD_VARIANTS_H__
+
+#include <stdint.h>
+
+enum mtl_boardid {
+	MTLP_DDR5_RVP = 0x01,
+	MTLP_LP5_T3_RVP = 0x02,
+	MTLP_LP5_T4_RVP = 0x04,
+	MTLM_LP5_RVP = 0x06,
+};
+
+#endif /*__BASEBOARD_VARIANTS_H__ */