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/socfpga_vining_fpga_defconfig b/configs/socfpga_vining_fpga_defconfig
index 3a99667..96c0ebb 100644
--- a/configs/socfpga_vining_fpga_defconfig
+++ b/configs/socfpga_vining_fpga_defconfig
@@ -88,6 +88,7 @@
 CONFIG_MISC=y
 CONFIG_I2C_EEPROM=y
 CONFIG_SYS_I2C_EEPROM_ADDR=0x50
+CONFIG_SYS_MMC_MAX_BLK_COUNT=256
 CONFIG_MMC_DW=y
 CONFIG_MTD=y
 CONFIG_SF_DEFAULT_SPEED=40000000