ppc: Split MPC83xx SERDES code from MPC85xx/MPC86xx/QorIQ

The MPC83xx SERDES control is different from the other FSL PPC chips.
For now lets split it out so we can standardize on interfaces for
determining of a device on SERDES is configured.

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