MIPS: rb532: move GPIOD definition into C-files

MIPS: rb532: move GPIOD definition into C-files

My kernel robot reports build error from drivers/iio/adc/da9150-gpadc.c,

  drivers/iio/adc/da9150-gpadc.c:254:13: error: ‘DA9150_GPADC_CHAN_0x08’
  undeclared here (not in a function); did you mean ‘DA9150_GPADC_CHAN_TBAT’?
     254 |  .channel = DA9150_GPADC_CHAN_##_id,

We define GPIOD in rb.h, in fact it should only be used in gpio.c, but
it affects the driver da9150-gpadc.c which goes against the original
intention of the design, just move it to its scope.

Fixes: 1b432840d0a4 ("MIPS: RB532: GPIO register offsets are relative to GPIOBASE")
Suggested-by: Jonathan Cameron <jic23@kernel.org>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reported-by: k2ci <kernel-bot@kylinos.cn>
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>