mb/asus/maximus_iv_gene-z: Select NO_UART_ON_SUPERIO

This board doesn't have a UART on the super I/O. Selecting this option
speeds up boot time from ~493 ms to ~416 ms.

Change-Id: I1d84f373831381da79022638e1082adf68f47aad
Signed-off-by: Tristan Corrick <tristan@corrick.kiwi>
Reviewed-on: https://review.coreboot.org/c/30148
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/asus/maximus_iv_gene-z/Kconfig

@@ -28,6 +28,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select INTEL_INT15
 	select MAINBOARD_HAS_LIBGFXINIT
 	select NORTHBRIDGE_INTEL_SANDYBRIDGE
+	select NO_UART_ON_SUPERIO
 	select SERIRQ_CONTINUOUS_MODE
 	select SOUTHBRIDGE_INTEL_BD82X6X
 	select SUPERIO_NUVOTON_NCT6776