drm/i915/debugfs: Move out pipe CRC code

In preparation to using a generic API in the DRM core for continuous CRC
generation, move the related code out of i915_debugfs.c into a new file.

Eventually, only the Intel-specific code will remain in this new file.

v2: Rebased.

v6: Rebased.

v7: Fix whitespace issue.

v9: Have intel_display_crc_init accept a drm_i915_private instead.

v12: Rebased.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1481545788-18194-1-git-send-email-tomeu.vizoso@collabora.com