mmc: esdhc: Add support for 8-bit bus width and non-removable card

This patch adds support of connecting an MMC media using an 8-bit
bus width connection to Freescale's P2020 H/W SDHC controller. During
the probe function, the generic function mmc_of_parse is called to
detect whether the controller is configured with 8-bit bus width.

Also, the generic function detects if the non-removable property is
set in the device tree.  The function esdhc_pltfm_bus_width was added
because the bus width configuration is platform specific.

Signed-off-by: Oded Gabbay <ogabbay@advaoptical.com>
Reviewed-by: Anton Vorontsov <anton@enomsg.org>
Signed-off-by: Chris Ball <cjb@laptop.org>