src/ec/intel: Create common code for board_id implementation

This patch creates initial common code structure for board_id
implementation for intel rvp platforms. Board_id helps in
identifying the platform with respect to CHROME_EC and INTEL_EC
(Windows_EC). Changes include
1. Create initial board_id.c and board_id.h
2. Modify the Makefile to include src/ec/intel directory

BUG=b:260654043
TEST=Able to build with the patch and boot the mtlrvp platform with the
subsequent patches in the train

Signed-off-by: Harsha B R <harsha.b.r@intel.com>
Change-Id: If133f6a72b8c3e1d8811a11f91e4556beb8c16e0
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70227
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Reviewed-by: Usha P <usha.p@intel.com>
Reviewed-by: Subrata Banik <subratabanik@google.com>

Makefile.inc

@@ -80,6 +80,7 @@ PHONY+= clean-abuild coreboot check-style build_complete
 #######################################################################
 # root source directories of coreboot
 subdirs-y := src/lib src/commonlib/ src/console src/device src/acpi src/superio/common
+subdirs-$(CONFIG_EC_ACPI) += src/ec/intel
 subdirs-y += src/ec/acpi $(wildcard src/ec/*/*) $(wildcard src/southbridge/*/*)
 subdirs-y += $(wildcard src/soc/*) $(wildcard src/soc/*/common) $(filter-out $(wildcard src/soc/*/common),$(wildcard src/soc/*/*))
 subdirs-y += $(wildcard src/northbridge/*/*)