drm/i915: Don't enable display error interrupts from the start

We need to enable interrupt processing before all the modeset
state is set up. But that means we can fall over when we get a pipe
underrun. This shouldn't happen as long as the bios works correctly
but as usual this turns out to be wishful thinking.

So disable error interrupts at irq install time and rely on the
re-enabling code in the modeset functions to take care of this.

Note that due to the SDE interrupt handling race we must
uncondtionally enable all interrupt sources in SDEIER, hence no need
to enable the SERR bit specifically.

On gmch platforms we don't have an explicit enable/mask bit for fifo
underruns. Fixing this up would require a bit of software tracking,
hence is material for a separate patch. To make this possible we need
to switch all gmch platforms to the new pipestat interrupt handling
scheme Imre implemented for vlv, and then also add a safe form of sw
state checking to __cpu_fifo_underrun_reporting_enabled a bit.

v2: Also handle the ilk/snb cpu fifo underrun bits accordingly.
Spotted by Ville.

v3: Also handle the south interrupt underrun bits on ibx. Again
spotted by Ville.

Reported-by: Rob Clark <robdclark@gmail.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: stable@vger.kernel.org
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>