uboot: disable hs200 mode to fix emmc detection on cn9132 cex7

There is some buggy logic in selecting emmc modes where once a uhs mode
was tried all lower modes fail.

If however only DDR and SDR modes are attempted, then the SDR at 52MHz
succeeds.

Author: Josua-SR

configs/u-boot/cn913x_additions.config

@@ -34,3 +34,4 @@ CONFIG_CMD_WDT=y
 CONFIG_SPI_FLASH_WINBOND=y
 # CONFIG_ENV_SPI_MAX_HZ is not set
 # CONFIG_MMC_BROKEN_CD is not set
+# CONFIG_MMC_HS200_SUPPORT is not set