Revert "i965: Always use Y-tiled buffers on SKL+"

Revert "i965: Always use Y-tiled buffers on SKL+"

This commit broke Weston, Mutter, and xf86-video-modesetting, on KMS.

In order to use Y-tiled buffers, the kernel requires the tiling mode to
be explicitly named through the I915_FORMAT_MOD_Y_TILED AddFB2 modifier;
it disallows any attempt to infer the buffer's tiling mode.

As the GBM API does not have a way to extract modifiers for a buffer,
this commit broke all users of GBM on SKL+. Revert it for now, until we
get a way to extract modifier information from GBM, and also let GBM
users inform the implementation that it intends to use the modifiers.

This reverts commit 6a0d036483caf87d43ebe2edd1905873446c9589.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Acked-by: Ben Widawsky <ben@bwidawsk.net>
Tested-by: Hans de Goede <hdegoede@redhat.com>