power: smb1355: Force enable Bandgap while charging is active

To optimize on power the SMB hardware disables the Bandgap
when the charger is removed. When this happens, the SMB1355 IRQ
line stays stuck in its last known state. I.e. if there was an
interrupt pending (the IRQ line is low) and if the Bandgap gets
disabled, the line stays stuck low forever causing a storm of
interrupts.

Fix this by forcing the Bandgap on as long as the parallel
charger is enabled. Also, disable the registered SMB IRQs before
the Bandgap is disabled by software.

CRs-Fixed: 2160392
Change-Id: I237f438da439f4cf3c45ff812e6121e83bd050c1
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>