leds: qpnp-wled: add support for configuring ILIM in pmicobalt

Currently, current limit (ILIM) for WLED is configured only for
pmi8994. ILIM levels differs in pmicobalt. Also, the step size
assumed before cannot go well with the different levels.
Default ILIM value differs for LCD and AMOLED mode. Taking this
all into account, add a separate function to configure ILIM for
different PMIC subtypes.

Change-Id: Ibc69706ae1dc878de5cbdaf283f0d71aff8000a1
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>