mmc: fsl_esdhc: drop CONFIG_SYS_FSL_ESDHC_FORCE_VSELECT

CONFIG_SYS_FSL_ESDHC_FORCE_VSELECT is not the correct method
to set I/O to 1.8. To boards that does not support vqmmc-supply,
use vs18_enable in fsl_esdhc_cfg. If regulator is supported,
use fixed 1.8V regulator for vqmmc-supply.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: York Sun <york.sun@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>