msm_serial: Send more than 1 character at a time on UARTDM
UARTDM cores have a TX fifo that can accept more than one
character per register write, but the msm_serial driver currently
only supports 1 character mode. Add support for this mode of operation
to speed up the transmit path on DM devices.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> Acked-by: David Brown <davidb@codeaurora.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>