power: bcl: Unregister SoC when BCL is disabled

Unregister the State of Charge (SoC) change
notification, when BCL monitoring is disabled.
This potentially has a corner case, where SoC
change can still trigger mitigation when BCL
is disabled.

CRs-Fixed: 808567
Change-Id: Iea7237f0a9a86b7420084252bdea658cd93e7e2f
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>