I.MX6 support eMMC 5.0

/*****************************************************************************
 *                         I.MX6 support eMMC 5.0
 * 说明：
 *     看一下支持eMMC 5.0的支持情况。
 *
 *                                            2017-5-16 台湾 中和区 曾剑锋
 ****************************************************************************/

一、参考文档：
    . EMMC 5.0 and EMMC 5.1 work on i.MX6
        https://community.nxp.com/docs/DOC-332187

二、报错信息：
    mmc0: unrecognised EXT_CSD revision
    mmc0: error - whilst initialising MMC card

三、解决方法：
    . cat drivers/mmc/core/mmc.c :
        ...
        if (card->ext_csd.rev > ) {    // The '6' has to be replaced with '7' For EMMC5.0
                                        // The '6' has to be replaced with '8'  For EMMC5.1
            pr_err("%s: unrecognised EXT_CSD revision %d\n",
            mmc_hostname(card->host), card->ext_csd.rev);
            err = -EINVAL;
            goto out;
        }
        ...