drm/i915/psr: Control PSR interrupts via debugfs

Interrupts other than the one for AUX errors are required only for debug,
so unmask them via debugfs when the user requests debug.

User can make such a request with
echo 1 > <DEBUG_FS>/dri/0/i915_edp_psr_debug

There are no locks to serialize PSR debug enabling from
irq_postinstall() and debugfs for simplicity. As irq_postinstall() is
called only during module initialization/resume and IGT subtests
aren't expected to modify PSR debug at those times, we should be safe.

v2: Unroll loops (Ville)
    Avoid resetting error mask bits.

v3: Unmask interrupts in postinstall() if debug was still enabled.
    Avoid RMW (Ville)

v4: Avoid extra IMR write introduced in the previous version.(Jose)
    Style changes, renames (Jose).

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Jose Roberto de Souza <jose.souza@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405013717.24254-1-dhinakaran.pandiyan@intel.com

drivers/gpu/drm/i915/intel_drv.h

@@ -1899,6 +1899,8 @@ void intel_psr_single_frame_update(struct drm_i915_private *dev_priv,
 				   unsigned frontbuffer_bits);
 void intel_psr_compute_config(struct intel_dp *intel_dp,
 			      struct intel_crtc_state *crtc_state);
+void intel_psr_irq_control(struct drm_i915_private *dev_priv, bool debug);
+void intel_psr_irq_handler(struct drm_i915_private *dev_priv, u32 psr_iir);
 
 /* intel_runtime_pm.c */
 int intel_power_domains_init(struct drm_i915_private *);