serial: sccnxp: Allow to use non-standard baud rates

This patch adds support for the use of non-standard baud rates.
For these purposes, we use the built-in timer/counter.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>