st/nine: Introduce STREAMFREQ state

st/nine: Introduce STREAMFREQ state

Previous vertex elements code update
was protected by
'if ((group & (NINE_STATE_VDECL | NINE_STATE_VS)) ||
state->changed.stream_freq & ~1)'
itself protected by
'if (group & (NINE_STATE_COMMON | NINE_STATE_VS))'

If no state is changed except the stream frequency,
no update would happen.

This patch solves the problem by adding a new
NINE_STATE_STREAMFREQ state.
Another way would be to add state->changed.stream_freq & ~1
check to the main test.

Signed-off-by: Axel Davy <axel.davy@ens.fr>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>