mmc: fsl_esdhc: Set fallback mode to 1-bit

mmc: fsl_esdhc: Set fallback mode to 1-bit

8-bit mode is not supported by SD cards and on P2020 are four SDHC pins
shared with SPI (so if P2020 board have also SPI then only 4-bit SDHC mode
is provided). So 8-bit SDHC mode is really bad default.

When max bus width is not provided then set mode to 1-bit. This mode is
supported by all cards, so it is the best option for fallback mode.

Also P2020 bootrom sets mode to 1-bit when booting from SD/MMC card.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>