tty: serial: msm: Add msm prefix to all driver functions

Make function naming consistent across this driver.
Also rename msm_irq to msm_uart_irq. No functional changes.

Signed-off-by: Ivan T. Ivanov <ivan.ivanov@linaro.org>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>