This patch is to clean up bus width setting code.

- For DM_MMC, remove getting "bus-width" from device tree.
  This has been done in mmc_of_parse().

- For non-DM_MMC, move bus width configuration from fsl_esdhc_init()
  to fsl_esdhc_initialize() which is non-DM_MMC specific.
  And fix up bus width configuration to support only 1-bit, 4-bit,
  or 8-bit. Keep using 8-bit if it's not set because many platforms
  use driver without providing max bus width.

- Remove bus_width member from fsl_esdhc_priv structure.
Signed-off-by: NYangbo Lu <yangbo.lu@nxp.com>