Convert CONFIG_SYS_MMC_MAX_BLK_COUNT to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MMC_MAX_BLK_COUNT

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index 56f4282..bf4d994 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -93,6 +93,13 @@
 	  are enabled by default, other may require additional flags or are
 	  enabled by the host driver.
 
+config SYS_MMC_MAX_BLK_COUNT
+	int "Block count limit"
+	default 65535
+	help
+	  The block count limit on MMC based devices. We default to 65535 due
+	  to a 16bit register limit on some hardware.
+
 config MMC_HW_PARTITIONING
 	bool "Support for HW partitioning command(eMMC)"
 	default y