serial: msm_geni_serial: Extend packing configurations

Currently packing configuration is done for 8bits per
transfer word as default as part of baud rate change.

Extend packing configuration when there is a request for
5bits/6bits/7bits per transfer word from set_termios.

Change-Id: I01341c94eef3b3697db3fce7846042cbe9e9f2af
Signed-off-by: Visweswara Tanuku <quic_vtanuku@quicinc.com>