cxgbe(4): Skip a few more T5/T6 registers during a regdump.
These registers have read side effects and a read at just the right
(wrong?) time can trash some internal hw state.
Obtained from: Chelsio Communications
Sponsored by: Chelsio Communications
(cherry picked from commit f13920b39b8b500a17fc276629d70828f9f2d4b1)