soc/intel/cannonlake: Reduce STACK_SIZE to 4KiB

TEST=Build and boot cannonlake rvp till OS.

Change-Id: I5369afd0d1d66e25d210416730a2c1c91ca8e94a
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/26345
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/cannonlake/Kconfig

@@ -231,10 +231,6 @@ config C_ENV_BOOTBLOCK_SIZE
 	hex
 	default 0x8000
 
-config STACK_SIZE
-	hex
-	default 0x2000
-
 choice
 	prompt "Cache-as-ram implementation"
 	default USE_CANNONLAKE_CAR_NEM_ENHANCED if MAINBOARD_HAS_CHROMEOS