mmc: spl: select SPL_BLK for SPL_DM_MMC

mmc_bind() in mmc-uclass.c calls blk_create_devicef() which is
defined in blk-uclass.c, so SPL_BLK is required by SPL_DM_MMC.
Implicitly select SPL_BLK for SPL_DM_MMC.

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index 726c8d8..17618c3 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -46,6 +46,7 @@
 	depends on SPL_DM && DM_MMC
 	default n if ARCH_MVEBU && !MVEBU_SPL_BOOT_DEVICE_MMC
 	default y
+	select SPL_BLK
 	help
 	  This enables the MultiMediaCard (MMC) uclass which supports MMC and
 	  Secure Digital I/O (SDIO) cards. Both removable (SD, micro-SD, etc.)