serial: New serial driver SCCNXP

This driver is a replacement for a SC26XX driver with a lot of
improvements and new features.
The main differences from the SC26XX driver:
- Removed dependency on MIPS. Driver can be used on any platform.
- Added support for SCC2681, SCC2691, SCC2692, SC28L91, SC28L92,
  SC28L202, SCC68681 and SCC68692 ICs.
- Using devm_-related functions.
- Improved error handling of serial port, improved FIFO handling.
- Ability to load multiple instances of drivers.

To avoid the possibility of regression, driver SC26XX left in the
system to confirm the stability of the driver on platforms where
it is being used.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>