serial: msm_geni_serial: Add 4-wire UART functionality

Add functionality pertinent to 4-wire UART which enables flow control
functionality for the High Speed usecases.

Change-Id: I35e8aa39c0dd6017d63c3450c830786992aae3e0
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>
4 files changed