regulator: qcom_spmi: Add slewing delays for all SMPS types

Only the FT SMPS type regulators have slewing supported in the
driver, but all types of SMPS regulators need the same support.
The only difference is that some SMPS regulators don't have a
step size and the step delay is typically 20, not 8. Luckily, the
step size reads as 0 for the non-FT types, so we can always read
that, but we need to detect which type of regulator we're using
to figure out what step delay to use. Make these minor
adjustments to the slew rate calculations and add support for the
delay function to the appropriate regulator ops.

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