drm/bridge/adv7511: Delay clearing of HPD interrupt status

When a hotplug event occurs, the adv7511 interrupt handler schedules
an hpd work after clearing the interrupt status registers
(ADV7511_REG_INT(x). The hpd work calls a drm helper that sends a
uevent to notify the userspace about the hotplug event.

On a hotplug connect, the userspace generally acts upon this uevent by
calling an ioctl (DRM_IOCTL_MODE_GETCONNECTOR) that probes on the
connector.This results in the connector's detect() drm_connector_func
being called. In the ADV7511 driver, this is a wrapper around the
adv7511_detect() call.

adv7511_detect() checks on the same interrupt ADV7511_REG_INT(0)
register which was previously cleared by the interrupt handler,
resulting in the func not realizing that a hotplug connect event
took place. ADV7511 loses its state when a disconnect happens, and
the driver needs to do a power-on to re-enable the hardware. This
fails to happen since calls to adv7511_detect() can fail to identify
that a hotplug connect took place.

Fix this by delaying the clearing of the ADV7511_INT0_HPD status flag.
Let the call to adv7511_hpd() be the only one responsible for clearing
this bitfield.

Note: Not sure if this is the best approach. Clearing a status flag
outside of the interrupt handler is generally looked down upon.

Signed-off-by: Archit Taneja <architt@codeaurora.org>