mesa: fix SwapBytes handling in numerous places
In a number of places the SwapBytes handling didn't handle cases with
GL_(UN)PACK_ALIGNMENT set and 7 byte width cases aligned to 8 bytes.
This adds a common routine to swap bytes a 2D image and uses this
code in:
texture storage
texture get
readpixels
swrast drawpixels.
[airlied: updated with Brian's nitpicks].
Cc: "11.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
(cherry picked from commit
0ad3a475ef81dad3baf607d749b91dfa1700ca23)