gpio: pca953x: Improve bias setting

The commit 15add068 ("gpio: pca953x: add ->set_config implementation")
introduced support for bias setting. However this, due to being half-baked,
brought potential issues:
 - the turning bias via disabling makes the pin floating for a while;
 - once enabled, bias can't be disabled.

Fix all these by adding support for bias disabling and move the disabling
part under the corresponding conditional.

While at it, add support for default setting, since it's cheap to add.

Fixes: 15add068

 ("gpio: pca953x: add ->set_config implementation")
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>