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/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 724b0e3..5ba35bb 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -409,7 +409,7 @@
 static const intel_limit_t intel_limits_bxt = {
 	/* FIXME: find real dot limits */
 	.dot = { .min = 0, .max = INT_MAX },
-	.vco = { .min = 4800000, .max = 6480000 },
+	.vco = { .min = 4800000, .max = 6700000 },
 	.n = { .min = 1, .max = 1 },
 	.m1 = { .min = 2, .max = 2 },
 	/* FIXME: find real m2 limits */