drm/i915: Fix CRT hotplug regression in 2.6.35-rc1

Commit 7a772c49 has two bugs which
made the hotplug problems on my laptop worse instead of better.

First, it did not, in fact, disable the CRT plug interrupt -- it
disabled all the other hotplug interrupts.  It seems rather doubtful
that that bit of the patch fixed anything, so let's just remove it.
(If you want to add it back, you probably meant ~CRT_HOTPLUG_INT_EN.)

Second, on at least my GM45, setting CRT_HOTPLUG_ACTIVATION_PERIOD_64
and CRT_HOTPLUG_VOLTAGE_COMPARE_50 (when they were previously unset)
causes a hotplug interrupt about three seconds later.  The old code
never restored PORT_HOTPLUG_EN so this could only happen once, but
they new code restores those registers.  So just set those bits when
we set up the interrupt in the first place.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Signed-off-by: Eric Anholt <eric@anholt.net>