Convert CONFIG_BOOTCOUNT_LIMIT to Kconfig

This converts the following to Kconfig:
   CONFIG_BOOTCOUNT_LIMIT

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Tested-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Hannes Schmelzer <hannes.schmelzer@br-automation.com>
Acked-by: Hannes Schmelzer <hannes.schmelzer@br-automation.com>
diff --git a/configs/am335x_boneblack_vboot_defconfig b/configs/am335x_boneblack_vboot_defconfig
index 016ec4e..df73f65 100644
--- a/configs/am335x_boneblack_vboot_defconfig
+++ b/configs/am335x_boneblack_vboot_defconfig
@@ -26,6 +26,7 @@
 CONFIG_OF_CONTROL=y
 CONFIG_ENV_IS_IN_MMC=y
 # CONFIG_BLK is not set
+CONFIG_BOOTCOUNT_LIMIT=y
 CONFIG_DFU_MMC=y
 CONFIG_DFU_RAM=y
 CONFIG_DM_I2C=y