mb/asrock/z97_extreme6: Fix EDID mapping for DVI-I

This board has a DVI-I connector, which supports both digital and analog
display outputs. The I2C bus to retrieve the EDID is shared between both
outputs, so `select GFX_GMA_ANALOG_I2C_HDMI_B` to describe this.

Can't currently test this due to lack of hardware.

Change-Id: Ib8239917e2f7ee5bb982621752ec406c2d3ca302
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82753
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/mainboard/asrock/z97_extreme6/Kconfig

@@ -5,6 +5,7 @@ if BOARD_ASROCK_Z97_EXTREME6
 config BOARD_SPECIFIC_OPTIONS
 	def_bool y
 	select BOARD_ROMSIZE_KB_8192
+	select GFX_GMA_ANALOG_I2C_HDMI_B
 	select HAVE_ACPI_RESUME
 	select HAVE_ACPI_TABLES
 	select INTEL_GMA_HAVE_VBT