power: pm8921-charger: distinguish between PMIC 3.0.1 and 3.0

Some workarounds that are required for PMIC die version 3.0
differ slightly for die version 3.0.1.

Fix this by checking the PMIC subversion register to distinguish
between 3.0 and 3.0.1.

Change-Id: I415d7831f15c0d690fd118ff190cd710a31368c6
CRs-Fixed: 403150
Signed-off-by: David Keitel <dkeitel@codeaurora.org>