wip! i965: Make intel_miptree_get_image_offset 64-bit safe

48-bit addresses arrive in Broadwell. Let's stop assuming in i965 that
graphics addresses and offsets are always 32-bit. This patch is one
small step towards that direction.

This patch only changes the signature of intel_miptree_get_offset() ...

   void
   intel_miptree_get_image_offset(const struct intel_mipmap_tree *mt,
                                  GLuint level, GLuint slice,
  -                               GLuint *x, GLuint *y);
  +                               uintptr_t *x, uintptr_t *y);

... and updates the types of all function-scope variables passed to
that function.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>