drm/crc: Cleanup crtc_crc_open function

drm/crc: Cleanup crtc_crc_open function

This patch make changes to allocate crc-entries buffer before
enabling CRC generation.
It moves all the failure check early in the function before setting
the source or memory allocation.
Now set_crc_source takes only two variable inputs, values_cnt we
already gets as part of verify_crc_source.

Changes since V1:
 - refactor code to use single spin lock
Changes since V2:
 - rebase
Changes since V3:
 - rebase on top of VKMS driver

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Leo Li <sunpeng.li@amd.com> (V2)
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> (V3)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180821083858.26275-3-mahesh1.kumar@intel.com