pvr: Implement CmdEvent* APIs.

Merged Rajnesh Kanwal requested to merge rajnesh-kanwal/mesa:staging/implement_cmdevent into main

Signed-off-by: Rajnesh Kanwal rajnesh.kanwal@imgtec.com Signed-off-by: Karmjit Mahil Karmjit.Mahil@imgtec.com

/cc @frankbinns @CreativeCylon

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