OMAPDSS: HDMI: clean up PHY power handling

OMAPDSS: HDMI: clean up PHY power handling

The TRM tells to set PHY to TXON only after getting LINK_CONNECT, and to
set PHY to OFF or LDOON after getting LINK_DISCONNECT, in order to avoid
damage to the PHY.

We don't currently do it quite like that. Instead of using the HDMI
interrupts, we use HPD signal. This works, but is not actually quite
correct, as HPD comes at a different time than LINK_CONNECT and
LINK_DISCONNECT interrupts. Also, the HPD GPIO is a property of the TPD
level shifter, not HDMI IP, so handling the GPIO in the HDMI driver is
wrong.

This patch implements the PHY power handling correctly, using the
interrupts.

There is a corner case that causes some additional difficulties: we may
get both LINK_CONNECT and LINK_DISCONNECT interrupts at the same time.
This is handled in the code by retrying: turning off the PHY, clearing
the interrupt status, and re-enabling the PHY. This causes a new
LINK_CONNECT interrupt to happen if a cable is connected.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>