cc3200: Move UART peripheral clock enable into soc init

Previously, UART clock enable was done in pinmux init.

This is now moved into soc initialization, along with other
power related initialization routines.

Change-Id: I1f9464655ad966e9caac2d238006f12a06b202ab
Signed-off-by: Gil Pitney <gil.pitney@linaro.org>