meson: Add dependency on genxml to anvil genfiles

This fixes a race condition where anv_gen_files are executed before
genxml files, which causes a build failure

v2: add dependency on idep_genxml (Lionel)

Fixes: d1992255
       ("meson: Add build Intel "anv" vulkan driver")

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit b74e605c)