drm/i915: Separate cherryview from valleyview

The cherryview device shares many characteristics with the valleyview
device.  When support was added to the driver for cherryview, the
corresponding device info structure included .is_valleyview = 1.
This is not correct and leads to some confusion.

This patch changes .is_valleyview to .is_cherryview in the cherryview
device info structure and simplifies the IS_CHERRYVIEW macro.
Then where appropriate, instances of IS_VALLEYVIEW are replaced with
IS_VALLEYVIEW || IS_CHERRYVIEW or equivalent.

v2: Use IS_VALLEYVIEW || IS_CHERRYVIEW instead of defining a new macro.
    Also add followup patches to fix issues discovered during the first
    review. (Ville)
v3: Fix some style issues and one gen check. Remove CRT related changes
    as CRT is not supported on CHV. (Imre, Ville)
v4: Make a few more optimizations. (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Wayne Boyer <wayne.boyer@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449692975-14803-1-git-send-email-wayne.boyer@intel.com
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>