tty: serial: msm_geni_serial: Avoid polling for TX Done in HSUART

Polling for TX Done in HSUART instances leads to strict timing dependencies
which is unmet sometimes. This leads to prematurely aborting the data
transfer.

Handle the TX Done event in the interrupt mode itself.

CRs-Fixed: 2081036
Change-Id: I12a7494544c2215ea31a5e7890463f71b8a27e57
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>