mesa: add gl_context::NewDriverState and use it for vertex arrays

mesa: add gl_context::NewDriverState and use it for vertex arrays

The vbo module recomputes its states if _NEW_ARRAY is set, so it shouldn't use
the same flag to notify the driver. Since we've run out of bits in NewState
and NewState is for core Mesa anyway, we need to find another way.

This patch is the first to start decoupling the state flags meant only
for core Mesa and those only for drivers.

The idea is to have two flag sets:
- gl_context::NewState - used by core Mesa only
- gl_context::NewDriverState - used by drivers only (the flags are defined
                               by the driver and opaque to core Mesa)

It makes perfect sense to use NewState|=_NEW_ARRAY to notify the vbo module
that the user changed vertex arrays, and the vbo module in turn sets
a driver-specific flag to notify the driver that it should update its vertex
array bindings.

The driver decides which bits of NewDriverState should be set and stores them
in gl_context::DriverFlags. Then, Core Mesa can do this:
ctx->NewDriverState |= ctx->DriverFlags.NewArray;

This patch implements this behavior and adapts st/mesa.
DriverFlags.NewArray is set to ST_NEW_VERTEX_ARRAYS.

Core Mesa only sets NewDriverState. It's the driver's responsibility to read
it whenever it wants and reset it to 0.

Reviewed-by: Brian Paul <brianp@vmware.com>