drm/i915: Rewrite fb rotation GTT handling

Redo the fb rotation handling in order to:
- eliminate the NV12 special casing
- handle fb->offsets[] properly
- make the rotation handling easier for the plane code

To achieve these goals we reduce intel_rotation_info to only contain
(for each plane) the rotated view width,height,stride in tile units,
and the page offset into the object where the plane starts. Each plane
is handled exactly the same way, no special casing for NV12 or other
formats. We then store the computed rotation_info under
intel_framebuffer so that we don't have to recompute it again.

To handle fb->offsets[] we treat them as a linear offsets and convert
them to x/y offsets from the start of the relevant GTT mapping (either
normal or rotated). We store the x/y offsets under intel_framebuffer,
and for some extra convenience we also store the rotated pitch (ie.
tile aligned plane height). So for each plane we have the normal
x/y offsets, rotated x/y offsets, and the rotated pitch. The normal
pitch is available already in fb->pitches[].

While we're gathering up all that extra information, we can also easily
compute the storage requirements for the framebuffer, so that we can
check that the object is big enough to hold it.

When it comes time to deal with the plane source coordinates, we first
rotate the clipped src coordinates to match the relevant GTT view
orientation, then add to them the fb x/y offsets. Next we compute
the aligned surface page offset, and as a result we're left with some
residual x/y offsets. Finally, if required by the hardware, we convert
the remaining x/y offsets into a linear offset.

For gen2/3 we simply skip computing the final page offset, and just
convert the src+fb x/y offsets directly into a linear offset since
that's what the hardware wants.

After this all platforms, incluing SKL+, compute these things in exactly
the same way (excluding alignemnt differences).

v2: Use BIT(DRM_ROTATE_270) instead of ROTATE_270 when rotating
    plane src coordinates
    Drop some spurious changes that got left behind during
    development
v3: Split out more changes to prep patches (Daniel)
    s/intel_fb->plane[].foo.bar/intel_fb->foo[].bar/ for brevity
    Rename intel_surf_gtt_offset to intel_fb_gtt_offset
    Kill the pointless 'plane' parameter from intel_fb_gtt_offset()
v4: Fix alignment vs. alignment-1 when calling
    _intel_compute_tile_offset() from intel_fill_fb_info()
    Pass the pitch in tiles in
    stad of pixels to intel_adjust_tile_offset() from intel_fill_fb_info()
    Pass the full width/height of the rotated area to
    drm_rect_rotate() for clarity
    Use u32 for more offsets
v5: Preserve the upper_32_bits()/lower_32_bits() handling for the
    fb ggtt offset (Sivakumar)
v6: Rebase due to drm_plane_state src/dst rects

Cc: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470821001-25272-2-git-send-email-ville.syrjala@linux.intel.com
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>