power: qpnp-smbcharger: use source detect for usb detection

False USB undervoltage (USBIN_UV) interrupts can fire when the battery
voltage is above the AICL threshold (4.25V) - 180mV (about 4.07V) and
battery charging is not happening. When this happens, the charger
hardware will use the autoshutdown threshold for both USBIN_UV and
AICL. When a very weak charger collapses under these conditions, an
USBIN_UV interrupt will also be generated since the USBIN voltage
is below both thresholds. When this occurs, the AICL algorithm does not
limit the input current within the AICL deglitch period of 20 ms,
causing an USBIN_UV interrupt to be sent out.

Fix this by using only USBIN source detection interrupt (USBIN_SRC_DET)
for insertion and removals. USBIN_SRC_DET uses an 1V threshold, so it
is much safer in the case of weak chargers.

CRs-Fixed: 832406
Change-Id: I0b8724318d2991b83738fd54aa9acf8c1c811657
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>