drm/i915/bxt: BUNs related to port PLL

This patch contains changes based on 2 updates to the spec:
Port PLL VCO restriction raised up to 6700.
Port PLL now needs DCO amp override enable for all VCO frequencies.

v2: Sonika's review comment addressed
	- dcoampovr_en_h variable not required
Based on a discussion with Siva, the following changes have been made.
	- replace dco_amp var with #define BXT_DCO_AMPLITUDE
	- set pll10 in a single assignment

v3:
Move DCO amplitude default value to i915_reg.h. Suggested by Siva.

Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Reviewed-by: Sonika Jindal <sonika.jindal@intel.com> [v2]
[danvet: Spell out BUN since not everyone knows what this means.]
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 42ba1ef..ac8436f 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1215,6 +1215,7 @@
 #define  PORT_PLL_LOCK_THRESHOLD_MASK	(0x7 << PORT_PLL_LOCK_THRESHOLD_SHIFT)
 /* PORT_PLL_10_A */
 #define  PORT_PLL_DCO_AMP_OVR_EN_H	(1<<27)
+#define  PORT_PLL_DCO_AMP_DEFAULT	15
 #define  PORT_PLL_DCO_AMP_MASK		0x3c00
 #define  PORT_PLL_DCO_AMP(x)		(x<<10)
 #define _PORT_PLL_BASE(port)		_PORT3(port, _PORT_PLL_0_A,	\