gpio-usbdetect: Add debounce in VBUS detection handling

Currently the GPIO usbdetect driver calls set_property
as soon as it receives VBUS detection interrupt. If the
time between VBUS off and on is very less, this can cause
set_property and otg_sm_work to race, thereby causing
syncronisation issue and enumeration failure.

To fix this behavior, add some debounce time for VBUS
'on' case in the IRQ handler and move the charger
notification to bottom half.

Change-Id: I59da3b3e4bd639d2a79934d9cf93e4da29b2f46d
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>