dm: sandbox: Convert to use CONFIG_CMD_MMC_OPS

Update the sandbox MMC emulation to use driver model for MMC operations.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index 94253a6..6a1874a 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -1,5 +1,4 @@
 CONFIG_SYS_MALLOC_F_LEN=0x2000
-CONFIG_BLK=y
 CONFIG_MMC=y
 CONFIG_PCI=y
 CONFIG_DEFAULT_DEVICE_TREE="sandbox"
@@ -71,6 +70,7 @@
 CONFIG_DEBUG_DEVRES=y
 CONFIG_ADC=y
 CONFIG_ADC_SANDBOX=y
+CONFIG_BLK=y
 CONFIG_CLK=y
 CONFIG_CPU=y
 CONFIG_DM_DEMO=y
@@ -101,7 +101,7 @@
 CONFIG_PWRSEQ=y
 CONFIG_SPL_PWRSEQ=y
 CONFIG_SYSRESET=y
-CONFIG_DM_MMC=y
+CONFIG_DM_MMC_OPS=y
 CONFIG_SANDBOX_MMC=y
 CONFIG_SPI_FLASH_SANDBOX=y
 CONFIG_SPI_FLASH=y