tty: serial: qcom_geni_serial: Add support for flow control

Add support for flow control functionality in the GENI serial driver
and also support for non-console higher baud rate(upto 4Mbps) usecases.

Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>
Signed-off-by: Mohammed Khajapasha <mkhaja@codeaurora.org>
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>