serial: ns16550: Increase scope of ops functions

Increase scope of ops functions and do some clean up for usage in device
-specific UART drivers.

Remove the static functionality of ops functions and migrate certain macros
to header file for usage in device-specific drivers.

Signed-off-by: Gokul Praveen <g-praveen@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
2 files changed