regulator: qcom_spmi: Only use selector based regulator ops

Mixing raw voltage and selector based regulator ops is
inconsistent. This driver already supports some selector based
ops via the list_voltage and set_voltage_time_sel ops but it uses
raw voltage ops for get_voltage and set_voltage. This causes
problems for regulator_set_voltage() and automatic insertion of
slewing delays because set_voltage_time_sel() is only used if the
regulator ops are all selector based. Put another way, delays
aren't happening at all right now when we should be waiting for
voltages to settle. Let's move to pure selector based regulator
ops so that the delays are inserted properly.

Cc: Georgi Djakov <georgi.djakov@linaro.org>
Cc: David Collins <collinsd@codeaurora.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>