mb/lenovo/t430: Fix Dual Graphics

* Select ONBOARD_VGA_IS_PRIMARY in driver/lenovo/hybrid_graphics to fix
  disabling iGPU in 'Dual Graphics' on Lenovo T430.
* Remove ONBOARD_VGA_IS_PRIMARY in mainboards that already select
  DRIVERS_LENOVO_HYBRID_GRAPHICS.

Change-Id: I6594fbb957c9a8135fe670d38b5755adf29d2dff
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/33254
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/drivers/lenovo/hybrid_graphics/Kconfig

@@ -1,3 +1,5 @@
 config DRIVERS_LENOVO_HYBRID_GRAPHICS
 	bool
 	default n
+	# for dual graphics we need to set this
+	select ONBOARD_VGA_IS_PRIMARY