v6->v7:
1.Change my Signed-off-by from "Zhou Yanjie [off-list ref]"
  to "周琰杰 (Zhou Yanjie) [off-list ref]" because
  the old mailbox is in an unstable state.
2.Add "ingenic_chip_info.reg_offset", use it instead of having
  hardcoded, and add "PZ_BASE()" / "PZ_GID2LD()" macros, use it
  with "ingenic_chip_info.reg_offset" to simplify code related
  to shadow registers.
3.Simplify the code of the "ingenic_set_bias" function.