Enable va-driver only in Fedora

Upstream, va-drivers are symlinks to libgallium [1].

The mesa-va-driver package is not distributed in CentOS/RHEL because it
is not in the allow-list. However, now that its functionality is part of
libgallium, it is required to disable it explicitly.

Make "with_va" a Fedora only option.

[1] b51ea6a445

Resolves: https://issues.redhat.com/browse/RHEL-144488

mesa.spec

@@ -4,11 +4,11 @@
 %global with_vmware 1
 %global with_vulkan_hw 1
 %global with_vdpau 1
-%global with_va 1
 %if !0%{?rhel}
 %global with_r300 1
 %global with_r600 1
 %global with_opencl 1
+%global with_va 1
 %endif
 %if !0%{?rhel} || 0%{?rhel} >= 10
 %global with_nvk %{with_vulkan_hw}