drm/i915: Implement fbc_status "Compressing" info for all platforms

drm/i915: Implement fbc_status "Compressing" info for all platforms

The number of compressed segments has been available ever since
FBC2 was introduced in g4x, it just moved from the STATUS register
into STATUS2 on IVB.

For FBC1 if we really wanted the number of compressed segments we'd
have to trawl through the tags, but in this case since the code just
uses the number of compressed segments as an indicator whether
compression has occurred we can just check the state of the
COMPRESSING and COMPRESSED bits. IIRC the hardware will try to
periodically recompress all uncompressed lines even if they haven't
changed and the COMPRESSED bit will be cleared while the compressor
is running, so just checking the COMPRESSED bit might not give us
the right answer. Hence it seems better to check for both
COMPRESSED and COMPRESSING as that should tell us that the
compressor is at least trying to do something.

While at it move the IVB+ register define to the right place, unify
the naming convention of the compressed segment count masks, and
fix up the mask for g4x.

v2: s/ILK_DPFC_STATUS2/IVB_FBC_STATUS2/ (Paulo)

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk> # SNB
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com> # ilk+
Acked-by: Paulo Zanoni <paulo.r.zanoni@intel.com> # pre-ilk
Link: http://patchwork.freedesktop.org/patch/msgid/20170606124318.31755-1-ville.syrjala@linux.intel.com