serial: msm_geni_serial: Align to HW assisted flow control support

If client enables HW AUTOCTS mode then set UPSTAT_AUTOCTS,otherwise
serial core disables TX fully at the framework layer and
no communication happens.

Change-Id: Ied2bec705991aad16638f767c09f33ae4dbfafdf
Signed-off-by: Akash Asthana <akashast@codeaurora.org>