Pass globals as a bare pointer, same as it sued to be prior to split kernel rework.
AMD CPU platform and Intel OpenCL were complaining about this.
Perhaps we shouldn't pass globals as pointer at all, this isn't something what is
really portable and can cause issues on 32 bit perhaps.
Decoupled ray marching is not supported yet.
Transparent shadows are always enabled for volume rendering.
Changes in kernel/bvh and kernel/geom are from Sergey.
This simiplifies code significantly, and prepares it for
record-all transparent shadow function in split kernel.