mb/asrock/b85m_pro4/Kconfig: Default to 2 MiB CBFS

I often find myself having to increase the CBFS size so that TianoCore
fits. Raise the default CBFS size to 2 MiB to alleviate this issue.

Change-Id: I871bb95dee55cc5bad68bb6e71f89ddfa4823497
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/46488
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/asrock/b85m_pro4/Kconfig

@@ -18,6 +18,10 @@ config BOARD_SPECIFIC_OPTIONS
 	select SOUTHBRIDGE_INTEL_LYNXPOINT
 	select SUPERIO_NUVOTON_NCT6776
 
+config CBFS_SIZE
+	hex
+	default 0x200000
+
 config MAINBOARD_DIR
 	string
 	default "asrock/b85m_pro4"