msm_serial: Add support for non-GSBI UARTDM devices

Not all UARTDM hardware is part of a GSBI complex. Add support
for these devices and fix a bug where we assumed uartdm meant the
hardware was part of a GSBI complex.

Cc: David Brown <davidb@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>