Convert CONFIG_HSMMC2_8BIT to Kconfig

This converts the following to Kconfig:
   CONFIG_HSMMC2_8BIT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am57xx_evm_defconfig b/configs/am57xx_evm_defconfig
index 054e974..03f7995 100644
--- a/configs/am57xx_evm_defconfig
+++ b/configs/am57xx_evm_defconfig
@@ -92,6 +92,7 @@
 CONFIG_SYS_I2C_EEPROM_ADDR=0x50
 CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_MMC_OMAP_HS=y
+CONFIG_HSMMC2_8BIT=y
 CONFIG_MTD=y
 CONFIG_DM_SPI_FLASH=y
 CONFIG_SF_DEFAULT_SPEED=76800000