drm/i915/bxt: BLC implementation

Enabling BLC on BXT.
Includes register definition, and new functions for BXT.

In BXT, there are 2 sets of registers for BLC. Until there is clarity
about which set would be effective, set 1 is being used.
This would have to be re-visited if there is any change or when 2 LFPs are
enabled on BXT.

This patch enables brightness change which would be effected by use of
hot-keys or sysfs entry.

TODO:- BLC implementation will have to re-visited when
1. there is clarity about which set of registers has to be used and when.
2. CDCLK frequency is changed

v2: Jani's review comments
	- Modified comment in i915_reg.h
	- Renamed register defintions
	- Removed definition of duty cycle max. Not required now and its not 64-bit.

v3:
  - Rebase on top of VLV/CHV backlight changes, in particuliar
    bxt_set_backlight() now has a different prototype (Damien)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Shankar, Uma <uma.shankar@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index ea5ca447..9447b27 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -3486,6 +3486,18 @@
 #define UTIL_PIN_CTL		0x48400
 #define   UTIL_PIN_ENABLE	(1 << 31)
 
+/* BXT backlight register definition. */
+#define BXT_BLC_PWM_CTL1			0xC8250
+#define   BXT_BLC_PWM_ENABLE			(1 << 31)
+#define   BXT_BLC_PWM_POLARITY			(1 << 29)
+#define BXT_BLC_PWM_FREQ1			0xC8254
+#define BXT_BLC_PWM_DUTY1			0xC8258
+
+#define BXT_BLC_PWM_CTL2			0xC8350
+#define BXT_BLC_PWM_FREQ2			0xC8354
+#define BXT_BLC_PWM_DUTY2			0xC8358
+
+
 #define PCH_GTC_CTL		0xe7000
 #define   PCH_GTC_ENABLE	(1 << 31)