soc/intel/cannonlake: Disable UART_DEBUG by default

This patch ensures serial debug is not enabled by default on Cannonlake
platform.

Change-Id: Id925c8c73971a027e45ea3c61e878f134bc9feff
Signed-off-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-on: https://review.coreboot.org/27205
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/cannonlake/Kconfig

@@ -64,7 +64,7 @@ config CPU_SPECIFIC_OPTIONS
 
 config UART_DEBUG
 	bool "Enable UART debug port."
-	default y
+	default n
 	select CONSOLE_SERIAL
 	select BOOTBLOCK_CONSOLE
 	select DRIVERS_UART