power: pm8921-bms: remove support for pm8921 v1.0 and v1.1

The bms module is reused in multiple pmics. It is now unnecessary
to check for 8921 versions in the driver. As a result of this change
older 8921 versions are not supported.

CRs-Fixed: 372679
Change-Id: Ie9131d47ed08fa6fa39812c9e60be34cc6280e4c
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>