[POWERPC] 83xx: Handle mpc8360 rev. 2.1 RGMII timing erratum

If on a rev. 2.1, adjust UCC clock and data timing characteristics
as specified in the rev.2.1 erratum #2.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>