drm/i915/bxt: Port PLL programming BUN

BUN 1: prop_coeff, int_coeff, tdctargetcnt programming updated and tied to
VCO frequencies. Program i_lockthresh in PORT_PLL_9.

VCO calculated based on the formula:
Desired Output = Port bit rate in MHz (DisplayPort HBR2 is 5400 MHz)
Fast Clock = Desired Output / 2
VCO = Fast Clock * P1 * P2

Prop_coeff, int_coeff, and tdctargetcnt modified according to above
calculation.

BUN 2: Port PLLs require additional programming at certain frequencies -
DCO amplitude in PORT_PLL_10

Review comments from Siva which were addressed in the initial version of the
patch.
	- Change PORT_PLL_LOCK_THRESHOLD to PORT_PLL_LOCK_THRESHOLD_MASK
	- Calculate for HDMI
	- Correct values for vco = 5.4
	- return in case of invalid vco range

v2: Imre's review comments addressed
	- change dcoampovr_en to dcoampovr_en_h
	- change PORT_PLL_DCO_AMP_OVR_EN to PORT_PLL_DCO_AMP_OVR_EN_H
	- Correct lane stagger value for 324MHz
	- Make coef common for HDMI and DP
	- remove superfluous comments

v3: Imre's comments addressed
	- Remove Prop_coeff, int_coeff, tdctargetcnt, dcoampovr_en, gain_ctl,
	dcoampovr_en_h from bxt_clk_div and make them local variables.

Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com> [v1]
Cc: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>