glsl/fp64: add helper for dual slot double detection.

glsl/fp64: add helper for dual slot double detection.

The old function didn't work for matrices, and we need this
in other places to fix some other problems, so move to a helper
in glsl type and fix the one user so far.

A dual slot double is one that has 3 or 4 components in it's
base type.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>