mesa: Use _mesa_lock_context_textures in _mesa_GetTexParameterfv()

mesa: Use _mesa_lock_context_textures in _mesa_GetTexParameterfv()

GetTexParamterfv() doesnt change texture state, so instead of
_mesa_lock_texture() we can use _mesa_lock_context_textures(),
which doesn't increase the texture stamp.  With this change,
_mesa_update_state_locked() is now only called from under
_mesa_lock_context_textures(), which is right thing to do.  Right now
it's the same mutex, but if we made texture locking more fine grained
locking one day, just locking one texture here would be wrong.

This all ignores the fact that texture locking seem a bit
flaky and broken, but we're trying to not blatantly make it worse.

This change allows us to reliably unlock the context textures in the
dd::UpdateState callback as is necessary for meta color resolves.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>