regulator: qpnp-lcdb: Replace revid checks with DT compatible properties

Define DT compatible strings to identify PMICs and use them instead of
externally querying the PMIC type. With this the driver does not have
any external API dependencies.
While at it, drop the support for PM660L rev < 2.

Change-Id: I7f2b8c12f1d0e74341e916fb7c51c02b63254885
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>