mb/bostentech/gbyt4: Increase default CBFS size to cover BIOS region

There is no reason to default to a 1MB CBFS when the descriptor gives us
5MB to work with.

Signed-off-by: Mate Kukri <km@mkukri.xyz>
Change-Id: I65a8b161c522a2da58420397aae6c7ff2b5cf30d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/86219
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/mainboard/bostentech/gbyt4/Kconfig

@@ -12,6 +12,9 @@ config BOARD_SPECIFIC_OPTIONS
 	select SOC_INTEL_BAYTRAIL
 	select SUPERIO_ITE_IT8728F
 
+config CBFS_SIZE
+	default 0x500000
+
 config MAINBOARD_DIR
 	default "bostentech/gbyt4"