x86: baytrail: Add SIO HS-UART clock setup

To support the BayTrail internal SIO HS UART, the internal UART clock
needs to get configured. This patch adds support for this clock
configuration which will be done, if the PCI device(s) are found.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>