mb/intel/tglrvp: Update MAINBOARD_PART_NUMBER

- Update MAINBOARD_PART_NUMBER for TGL variants
- MAINBOARD_PART_NUMBER is reported as FRID on acpi
- This is required for cros_config to differentiate
  across TGL variants.
- Mosys uses cros_config to identify TGL variants using
  data read from FRID

Bug=none
Test=build and boot coreboot on TGLRVP UP3 hardware

Signed-off-by: Anil Kumar <anil.kumar.k@intel.com>
Change-Id: I11d4ab2a5b6ade6c50988a9fec4d9866fe79d7b5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43620
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Wonkyu Kim <wonkyu.kim@intel.com>
Reviewed-by: Srinidhi N Kaushik <srinidhi.n.kaushik@intel.com>

src/mainboard/intel/tglrvp/Kconfig

@@ -46,7 +46,8 @@ config GBB_HWID
 
 config MAINBOARD_PART_NUMBER
 	string
-	default "tglrvp"
+	default "tglrvpu" if BOARD_INTEL_TGLRVP_UP3
+	default "tglrvpy" if BOARD_INTEL_TGLRVP_UP4
 
 config MAINBOARD_FAMILY
 	string