meson: Add dependency on genxml to anvil

Currently the Intel "anvil" driver races with the generation of genxml
files, while i965 has an explicit dependency. This patch adds the same
dependency to anvil.

Fixes: d1992255
       ("meson: Add build Intel "anv" vulkan driver")
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
(cherry picked from commit 279060cd)