drm/i915/psr: program vsc header for psr2

Function hsw_psr_setup handles vsc header setup for psr1 and
skl_psr_setup_vsc handles vsc header setup for psr2.

Setup VSC header in function skl_psr_setup_vsc for psr2 support,
as per edp 1.4 spec, table 6-11:VSC SDP HEADER Extension for psr2
operation.

v2: (Jani)
- Initialize variables to 0
- intel_dp_get_y_cord_status and intel_dp_get_y_cord_status made static
- Correct indentation for continuation lines
- Change DP_PSR_Y_COORDINATE to  DP_PSR2_SU_Y_COORDINATE_REQUIRED
- Change DPRX_FEATURE_ENUMERATION_LIST to DP_DPRX_*
- Change VSC_SDP_EXT_FOR_COLORIMETRY_SUPPORTED to DP_VSC_*

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: Vathsala Nagaraju <vathsala.nagaraju@intel.com>
Signed-off-by: Patil Deepti <deepti.patil@intel.com>
Reviewed-by: Jim Bride <jim.bride@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1483356663-32668-3-git-send-email-vathsala.nagaraju@intel.com