drm/i915: split intel_modeset_driver_remove() to pre/post irq uninstall

Split intel_modeset_driver_remove() to two, the part with working irqs
before irq uninstall, and the part after irq uninstall. Move
irq_unintall() closer to the layer it belongs.

The error path in i915_driver_modeset_probe() looks obviously weird
after this, but remains as good or broken as it ever was. No functional
changes.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200214135058.7580-1-jani.nikula@intel.com