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/configs/vexpress_ca9x4_defconfig b/configs/vexpress_ca9x4_defconfig
index 25e5d39..234686e 100644
--- a/configs/vexpress_ca9x4_defconfig
+++ b/configs/vexpress_ca9x4_defconfig
@@ -39,6 +39,7 @@
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_CLK=y
 CONFIG_ARM_PL180_MMCI=y
+CONFIG_SYS_MMC_MAX_BLK_COUNT=127
 CONFIG_MTD=y
 CONFIG_DM_MTD=y
 CONFIG_MTD_NOR_FLASH=y