serial: pic32_uart: Add PIC32 UART driver

This adds UART and a serial console driver for Microchip PIC32 class
devices.

[ralf@linux-mips.org: Resolved merge conflict.]

Signed-off-by: Andrei Pistirica <andrei.pistirica@microchip.com>
Signed-off-by: Joshua Henderson <joshua.henderson@microchip.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-serial@vger.kernel.org
Cc: linux-api@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12101/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>