power: smb135x-charger: enable usbin_uv and dcin_uv interrupt

The usbin_uv interrupt needs to be enabled because that is the only
way to reliable get notified when usb is removed. The current driver
relied on src_detect's falling edge and experiments have shown that
src_detect falling edge may not trigger when usb is removed.

While at it also enable the dcin_uv interrupt.

Change-Id: I1427a5aeb5a04acc16605e5b2bb24945252b4cb4
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>