drm/i915: s/intel_infoframe/gm45_infoframe

These two functions are actually hw-specific and only valid for gm45
thru gen7. HSW completely changes how this works, so label them
accordingly.

v2: s/gm45/g4x/ like for the previous patch.

Acked-by: Paulo Zanoni <przanoni@gmail.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>