drm/i2c: adv7511: Add HPD support

Add Hot Plug detect support for ADV7533. This involves:

1) Enabling the correct HPD interrupt enable registers in
   adv7511_power_on, adv7511_get_modes and adv7533_bridge_attach.
2) Flushing the irq stat registers in adv7511_irq_process only after
   we have called drm_helper_hpd_irq_event.
3) Getting rid of the HPD_ENABLE macro instances.
4) Add a 200 ms sleep in adv7511_get_modes after powering on the
   chip. This seems to be needed when we rely on EDID_READY
   interrupt to start reading EDID.

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