configure: omap, freedreno and tegra require atomics

They have used them since day one, but the check was never there.

v2:
 - Update the freedreno message (API is no longer experimental).
 - Move the freedreno host_cpu detection next to the intel one.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Thierry Reding <treding@nvidia.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>