drm/i915: Drop the 64k linear scanout alignment on gen2/3

drm/i915: Drop the 64k linear scanout alignment on gen2/3

The docs don't support the 64k linear scanout alignment we impose
on gen2/3. And it really makes no sense since we have no DSPSURF
register, so the only thing that the hardware will see is the linear
offset which will be just pixel aligned anyway.

There is one case where 64k comes into the picture, and that's FBC.
The start of the line length buffer corresponds to a 64k aligned
address of the uncompressed framebuffer. So if the uncompressed fb is
not 64k aligned, the first actually used entry in the line length
buffer will not be byte 0. There are 32 extra entries in the line
length buffer to account for this extra alignment so we shouldn't
have to worry about it when mapping the uncompressed fb to the GTT.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>