pinctrl: lochnagar: Don't build on MIPS

MIPS appears to define a RST symbol at a high level, which clashes
with some register naming in the driver. Since there is currently
no case for running this driver on MIPS devices simply cut off the
build of this driver on MIPS.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202311071303.JJMAOjy4-lkp@intel.com/


Suggested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20231115162853.1891940-1-ckeepax@opensource.cirrus.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>