meson: fix i965/anv/isl genX static lib names

Shouldn't make any functional difference, just that `liblibanv_gen90.a`
will now be called `libanv_gen90.a`.

Fixes: 3218056e "meson: Build i965 and dri stack"
Fixes: d1992255 "meson: Add build Intel "anv" vulkan driver"
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
(cherry picked from commit e8eb8482)

Trivial merge conflicts resolved by Dylan.