uart: Prepare to support multiple base addresses

Prepare low-level register access to take UART base address as a
parameter. This is done to support a list of base addresses defined
in the platform.

Change-Id: Ie630e55f2562f099b0ba9eb94b08c92d26dfdf2e
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/5309
Tested-by: build bot (Jenkins)
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
5 files changed