Create UART backend for logging SP

Create UART adapter and backend for the UART driver.

Signed-off-by: Gabor Toth <gabor.toth2@arm.com>
Signed-off-by: Gabor Ambrus <gabor.ambrus@arm.com>
Change-Id: Id3adec616599959b3a5777d665fcfcadf0ccb91b
6 files changed