mpc8308rdb: add support for eSDHC MMC controller

Add support for the onboard eSDHC MMC controller. The hardware on the
MPC8308RDB has the following errata:

- ESDHC111: manual asynchronous CMD12 is broken
- DMA is broken (PIO works)

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>

[added include fsl_esdhc header to prevent implicit declarations of
fsl_esdhc_mmc_init() and fdt_fixup_esdhc()]

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>