meson: Error building kmsro-required driver without kmsro

As I discovered while accidentally setting -Dgallium-drivers=panfrost, nothing in the build system fails with the combination of "driver requiring kmsro" and "no kmsro". Rather an inscrutable run time failure is raised that gives no insight into the missing dependency. So let's detect this case at build-time.

It's worth noting we can't simply set kmsro internally based on the driver list without changing behaviour, as it is possible to build freedreno with or without kmsro support. Rob and Eric says it's fine, so let's do that.

Signed-off-by: Alyssa Rosenzweig alyssa.rosenzweig@collabora.com