tty: serial: msm: Enable building msm_serial for ARCH_QCOM

We've split Qualcomm MSM support into legacy and multiplatform.  So add
the ability to build the serial driver on the newer ARCH_QCOM
multiplatform.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kumar Gala <galak@codeaurora.org>