mb/google/fatcat: Option to enable monochrome VGA mode 12

Update the Fatcat mainboard Kconfig to select
FSP_VGA_MODE12_MONOCHROME. The FSP_VGA_MODE12_MONOCHROME option enables
the use of a minimal 1-bit-per-pixel (1bpp) framebuffer for early
sign-of-life (eSOL) messages, which significantly reduces the DRAM size
required for the framebuffer in romstage.

Key changes:
- Deselect FSP_VGA_MODE12 for CONFIG_FATCAT_VGA_MODE12_SUPPORT.
- Select FSP_VGA_MODE12_MONOCHROME instead.

BUG=b:406725440
TEST=Verify VGA text rotation on Google/Felino.

Change-Id: I172f01b9766d2aa8e2f86c399ba46f6be008fed3
Signed-off-by: Kapil Porwal <kapilporwal@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90074
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Subrata Banik <subratabanik@google.com>

src/mainboard/google/fatcat/Kconfig

@@ -265,7 +265,7 @@ config FATCAT_VGA_MODE12_SUPPORT
 	default n
 	depends on FSP_UGOP_EARLY_SIGN_OF_LIFE
 	select ROMSTAGE_VGA
-	select FSP_VGA_MODE12
+	select FSP_VGA_MODE12_MONOCHROME
 	help
 	  Select this if the FSP supports VGA mode 12 for eSOL.