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/octeontx_83xx_defconfig b/configs/octeontx_83xx_defconfig
index bfd23fc..1afa6a3 100644
--- a/configs/octeontx_83xx_defconfig
+++ b/configs/octeontx_83xx_defconfig
@@ -84,6 +84,7 @@
 CONFIG_SYS_64BIT_LBA=y
 CONFIG_DM_I2C=y
 CONFIG_MISC=y
+CONFIG_SYS_MMC_MAX_BLK_COUNT=8192
 CONFIG_SUPPORT_EMMC_RPMB=y
 CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_MMC_OCTEONTX=y