x86: baytrail: Introduce a Kconfig option for the internal UART

There are quite a number of BayTrail boards that uses an external
SuperIO chipset to provide the legacy UART. For such cases, it's
better to have a Kconfig option to enable the internal UART.

So far BayleyBay and MinnowMax boards are using internal UART as
the U-Boot console, enable this on these two boards.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/minnowmax_defconfig b/configs/minnowmax_defconfig
index 28b837d..ba2b7dc 100644
--- a/configs/minnowmax_defconfig
+++ b/configs/minnowmax_defconfig
@@ -2,6 +2,7 @@
 CONFIG_VENDOR_INTEL=y
 CONFIG_DEFAULT_DEVICE_TREE="minnowmax"
 CONFIG_TARGET_MINNOWMAX=y
+CONFIG_INTERNAL_UART=y
 CONFIG_HAVE_INTEL_ME=y
 CONFIG_ENABLE_MRC_CACHE=y
 CONFIG_SMP=y