mb/intel/adlrvp: shorten MAINBOARD_PART_NUMBER to fix build

Building firmware for Brya is currently broken due to the RO_FWID region
for adlrvp_m_ext_ec bloating past 64 characters.

The CONFIG_MAINBOARD_PART_NUMBER is catenated onto the
CONFIG_MAINBOARD_VENDOR string, which for Intel, makes for a very long
trunk string that the kernel version will then be added to form the
RO_FWID string. For Intel, that trunk string is already pretty long at :
"Intel Corporation_Alder Lake Client Platform".

Shortening the CONFIG_MAINBOARD_PART_NUMBER should address this issue
for now.

BUG=b:241273391
TEST="emerge-brya coreboot chromeos-bootimage" and verify it builds
successfully

Change-Id: Ie862c87dd9a24743f249f1b10862ca6f3295db23
Signed-off-by: Nick Vaccaro <nvaccaro@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66397
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Bora Guvendik <bora.guvendik@intel.com>

src/mainboard/intel/adlrvp/Kconfig

@@ -113,7 +113,7 @@ config GBB_HWID
 	default "ADLRVPP"
 
 config MAINBOARD_PART_NUMBER
-	default "Alder Lake Client Platform"
+	default "Alder Lake Client"
 
 config MAINBOARD_VENDOR
 	string