Platform: Implement UART uninitialize function

This patch introduces an uninitialize function for the UART
peripheral to restore it's default state before passing
execution to runtime image from MCUBoot.

Change-Id: Iaf239b575be82402b9c142e990fb0ea30ffe9a88
Signed-off-by: David Vincze <david.vincze@arm.com>
5 files changed