drm/i915: Backlight control using CRC PMIC based PWM driver

Use the CRC PWM device in intel_panel.c and add new MIPI backlight
specififc callbacks

v2: Modify to use pwm_config callback
v3: Addressed Jani's comments
    - Renamed all function as pwm_* instead of vlv_*
    - Call intel_panel_actually_set_backlight in enable function
    - Return -ENODEV in case pwm_get fails
    - in case pwm_config error return error cdoe from pwm_config
    - Cleanup pwm in intel_panel_destroy_backlight
v4: Removed unused #defines and initialized backlight with INVALID_PIPE (Ville)

CC: Samuel Ortiz <sameo@linux.intel.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Shobhit Kumar <shobhit.kumar@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 1059283..2861270 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -182,6 +182,10 @@
 		bool enabled;
 		bool combination_mode;	/* gen 2/4 only */
 		bool active_low_pwm;
+
+		/* PWM chip */
+		struct pwm_device *pwm;
+
 		struct backlight_device *device;
 	} backlight;