drm/i915: Remove unused VLV/CHV PSR registers

PSR support for VLV and CHV was dropped in commit ce3508fd
("drm/i915/psr: Nuke PSR support for VLV and CHV") so no need to keep
this registers around.

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190406005112.27205-2-jose.souza@intel.com