tty: serial: uartlite: Support uartlite on big and little endian systems

Use big and little endian accessors function to reflect system configuration.
Detection is done via control register in ulite_request_port.

Tested on Microblaze LE, BE, PPC440 and Arm zynq.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>