MIPS: Loongson 1B: Add board support

MIPS: Loongson 1B: Add board support

Adds basic platform devices for Loongson 1B, including serial port,
ethernet, USB, RTC and interrupt handler.

The Loongson 1B UART is compatible with NS16550A, the Loongson 1B GMAC is
built around a Synopsys IP Core.

Use normal instead of enhanced descriptors.

Thanks to Giuseppe for updating the normal descriptor in stmmac driver.
Thanks to Zhao Zhang for implementing the RTC driver.

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: wuzhangjin@gmail.com
Cc: zhzhl555@gmail.com
Cc: Kelvin Cheung <keguang.zhang@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/4133/
Patchwork: https://patchwork.linux-mips.org/patch/4134/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>