vc4: Validate that the same BO doesn't get reused for different purposes.

vc4: Validate that the same BO doesn't get reused for different purposes.

We don't care if things like vertex data get smashed by render target
data, but we do need to make sure that shader code doesn't get rendered
to.

v2: Fix overflowing read of gl_relocs[] that incorrect flagged of some
    VBOs as shader code.