tty: serial: owl: Add support for kernel debugger

Implement 'poll_put_char' and 'poll_get_char' callbacks in struct
'owl_uart_ops' that enables OWL UART to be used for kernel debugging
over serial line.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Link: https://lore.kernel.org/r/026543195b9aeefb339d90abc5660a6ac7463c63.1610484108.git.cristian.ciocaltea@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>