power: smb135x-charger: use only usbin_uv/_ov for removal

The current driver uses both a falling edge on src_detect interrupt
or a rising edge on usbin_uv/_ov to initiate USB removal
activities. The src_detect is seen dropping even when a valid USB
is present.

Hence update the driver to use only usbin_uv/_ov interrupts for
USB removal.

CRs-Fixed: 631587
Change-Id: Iaa6c5853be8aa591721aea0b2fd5e4007de19f37
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>