powerpc/t208x: some update to support t2081

- fix serdes definition for t2081.
- fix clock speed for t2081.
- update ids, as CONFIG_FSL_SATA_V2 is needed only for t2080,
  T2081 has no SATA.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>