regulator: pbias: Fix broken pbias disable functionality

regulator_disable of pbias always writes '0' to the enable_reg.
However actual disable value of pbias regulator is not always '0'.
Fix it by populating the disable_val in pbias_reg_info for the
various platforms and assign it to the disable_val of
pbias regulator descriptor. This will be used by
regulator_disable_regmap while disabling pbias regulator.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: <stable@vger.kernel.org>