powerpc/85xx: Add eSDHC support on P2020DS

We enable SDHC_CD and SDHC_WP signals (pin muxed with GPIO8 & GPIO9
respectively).

We enable EXT2, FAT, and parition support for both MMC & USB configs.

Signed-off-by: Jerry Huang <Chang-Ming.Huang@freescale.com>
Signed-off-by: Jin Qing <b24347@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>