serial: msm_geni_serial: Add clock divider changes for UART sequencer

This patch adds changes introduced recently to reduce the sequencer's
samping to half the rate. This in turn doubles divider but in RUMI
for unknown reason it doesn't work straight away and works with
write-read-back clock divider registers, decision is taken based on
the dtsi flag of change-sampling-rate.

Change-Id: Ie02cb60fa8f9f9abf5af517dc68346a44d6e7ed4
Signed-off-by: Akash Asthana <akashast@codeaurora.org>
Signed-off-by: Mukesh Kumar Savaliya <msavaliy@codeaurora.org>