ASoC: rt286: Make RT286_SET_GPIO_* readable and writable

The GPIO configuration cannot be applied if the registers are inaccessible.
This prevented the headset mic from working on the Dell XPS 13 9343.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=114171
Signed-off-by: David Ward <david.ward@gatech.edu>
Link: https://lore.kernel.org/r/20210418134658.4333-5-david.ward@gatech.edu
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>