With geometry shaders the number of emitted primitived is decided
at run time, so we cannot precompute it in the CPU and we need to
use the PRIMITIVE_COUNTS_FEEDBACK commands to have the GPU provide
the number like we do for the number of primitives written to
transform feedback. This may have a performance impact though, since
it requires a sync wait for the draw to complete, so we only do
it when geometry shaders are present.

v2: remove '> 0' comparison for ponter type (Alejandro)

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>