mx6slevk: Fix MMC breakage for the SPL target

Commit 001cdbbb32 ("imx: mx6slevk: enable more DM drivers") breaks
MMC support in U-Boot proper on the mx6slevk_spl_defconfig target:

U-Boot SPL 2017.09-00396-g6ca43a5 (Oct 01 2017 - 16:20:18)
Trying to boot from MMC1

U-Boot 2017.09-00396-g6ca43a5 (Oct 01 2017 - 16:20:18 -0300)

CPU:   Freescale i.MX6SL rev1.0 792 MHz (running at 396 MHz)
CPU:   Commercial temperature grade (0C to 95C) at 33C
Reset cause: POR
Board: MX6SLEVK
I2C:   ready
DRAM:  1 GiB
MMC:   FSL_SDHC: 0
MMC Device 1 not found
*** Warning - No MMC card found, using default environment

As mx6slevk_spl_defconfig does not use CONFIG_DM_MMC and its
board file does not register the mmc controller for U-Boot proper,
let's fix this by adding CONFIG_DM_MMC=y and device tree support.

While at it, add more DM drivers, so that it becomes closer to
mx6slevk_defconfig.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>

configs/mx6slevk_spl_defconfig

@@ -9,7 +9,8 @@ CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_LIBDISK_SUPPORT=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y
 # CONFIG_CMD_BMODE is not set
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg,MX6SL,SYS_I2C"
+CONFIG_DEFAULT_DEVICE_TREE="imx6sl-evk"
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/mach-imx/spl_sd.cfg,MX6SL"
 CONFIG_BOOTDELAY=3
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL=y
@@ -32,13 +33,26 @@ CONFIG_CMD_EXT4=y
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_CMD_FAT=y
 CONFIG_CMD_FS_GENERIC=y
+CONFIG_OF_CONTROL=y
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_DM=y
+CONFIG_DM_GPIO=y
+CONFIG_DM_I2C=y
+CONFIG_DM_MMC=y
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_PHYLIB=y
+CONFIG_PINCTRL=y
+CONFIG_PINCTRL_IMX6=y
+CONFIG_DM_PMIC=y
+CONFIG_DM_PMIC_PFUZE100=y
+CONFIG_DM_REGULATOR=y
+CONFIG_DM_REGULATOR_PFUZE100=y
+CONFIG_DM_REGULATOR_FIXED=y
+CONFIG_DM_REGULATOR_GPIO=y
 CONFIG_DM_THERMAL=y
 CONFIG_USB=y
+CONFIG_DM_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_USB_HOST_ETHER=y
 CONFIG_USB_ETHER_ASIX=y