mb/intel/dg43gt: Select right gmbus port for VGA output

TESTED: NGI works on VGA with adapter on DVI-I port

Change-Id: I4bd9d451295d26a3e11ded9863f5d45d42c8fead
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/21441
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/intel/dg43gt/Kconfig

@@ -32,6 +32,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select HAVE_ACPI_RESUME
 	select INTEL_EDID
 	select MAINBOARD_HAS_NATIVE_VGA_INIT
+	select GFX_GMA_ANALOG_I2C_HDMI_C
 	select DRIVERS_I2C_CK505
 
 config VGA_BIOS_ID