uart: move baud rate and options into driver data

This moves the baud rate and options fields out of the UART driver
config struct and into the driver data struct. This will allow
changing baud rate and options at runtime in the future.

Change-Id: I62ddea2f95e634f2d60eeb9537f960799fc9301f
Signed-off-by: Daniel Leung <daniel.leung@intel.com>