anv/blit2d: Add a function to create an ImageView

This function differs from the open-coded implementation in that the
ImageView's width is determined by the caller and is not unconditionally
set to match the number of texels within the surface's pitch.

Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>