power: qpnp-fg: Add PMIC specific hw initialization

PMI8950 and PMI8994 have different hardware initialization
requirements. Split the hw_init function into common
and PMIC specific initialization.

Change-Id: Ibd68dc0c2b3458fe628989d2852899e56323c94a
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>