drm/i915: Unmask and enable master error interrupt on gen2/3

For whatever reason we only unmask and enable the master error
interrut on gen4. With the EIR handling fixed let's do that
on gen2/3 as well.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180611200258.27121-4-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>