mb/intel/mtlrvp: Enable EC MKBP device

MKBP device is required for passing events from input sources to AP.
Input sources include buttons (power, volume); switches (lid, tablet
mode) and sysrq.

BUG=b:342227155
TEST=Able to build coreboot for mtlrvp platform and switch tablet
     mode.

Change-Id: I630421c83784bb4492486d72290b9e8cdada1d47
Signed-off-by: Jay Patel <jay2.patel@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82612
Reviewed-by: Vijay P Hiremath <vijay.p.hiremath@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Ravishankar Sarawadi <ravishankar.sarawadi@intel.com>
Reviewed-by: Jamie Ryu <jamie.m.ryu@intel.com>

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

@@ -59,6 +59,9 @@
 /* Enable EC backed PD MCU device in ACPI */
 #define EC_ENABLE_PD_MCU_DEVICE
 
+/* Enable MKBP for buttons and switches */
+#define EC_ENABLE_MKBP_DEVICE
+
 /* Enable LID switch and provide wake pin for EC */
 #define EC_ENABLE_LID_SWITCH
 #define EC_ENABLE_WAKE_PIN	GPE_EC_WAKE