mb/google/guybrush: Set the ROMSIZE as 16M

Change-Id: Iec8b40bd89c25cd2193aff8af45d0a09b07ad6a3
Signed-off-by: Zheng Bao <fishbaozi@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49797
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/google/guybrush/Kconfig

@@ -7,6 +7,7 @@ if BOARD_GOOGLE_BASEBOARD_GUYBRUSH
 
 config BOARD_SPECIFIC_OPTIONS
 	def_bool y
+	select BOARD_ROMSIZE_KB_16384
 	select SOC_AMD_CEZANNE
 
 config FMDFILE