i965: Rename intel_miptree_get_dimensions_for_image()

i965: Rename intel_miptree_get_dimensions_for_image()

This function isn't specific to miptrees. So, drop the "miptree"
from function name.

V3: Add a comment explaining how the 1D Array texture height and
    depth is interpreted by Intel hardware.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>