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.