Add r1p12 to the list of supported Cadence UARTs. Xen only
uses the subset of features available in r1p8, so we don't
need to differentiate between r1p8 and r1p12 yet.
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com> Acked-by: Ian Campbell <ian.campbell@citrix.com>