MIPS: Alchemy: support multiple GPIO styles in one kernel

For GPIOLIB=y decide at runtime which gpiochips to register;
in the GPIOLIB=n case, the gpio headers need to be reshuffled
a bit to make multiple implementations coexist peacefully.

Signed-off-by: Manuel Lauss <manuel.lauss@googlemail.com>
To: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/2679/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>