regulator: pbias: Convert to use regulator_[enable|is_enabled]_regmap

Since commit ca5d1b35
"regulator: helpers: Modify helpers enabling multi-bit control",
we can set enable_val setting for device that use multiple bits for control
when using regmap enable/disable/bypass ops.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Balaji T K <balajitk@ti.com>
Signed-off-by: Mark Brown <broonie@linaro.org>