configure.ac: error out if building freedreno_kgsl without freedreno

The former is a subset of the latter. Error out early so the user is
aware that they are doing something very wrong.

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