Convert CONFIG_SYS_BOOTCOUNT_SINGLEWORD to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_BOOTCOUNT_SINGLEWORD

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Tested-by: Alex Kiernan <alex.kiernan@gmail.com>
Reviewed-by: Ian Ray <ian.ray@ge.com>
diff --git a/configs/highbank_defconfig b/configs/highbank_defconfig
index ec7bc8e..ee34a92 100644
--- a/configs/highbank_defconfig
+++ b/configs/highbank_defconfig
@@ -26,6 +26,7 @@
 CONFIG_ENV_IS_IN_NVRAM=y
 CONFIG_SCSI_AHCI=y
 CONFIG_BOOTCOUNT_LIMIT=y
+CONFIG_SYS_BOOTCOUNT_SINGLEWORD=y
 # CONFIG_MMC is not set
 CONFIG_SCSI=y
 CONFIG_OF_LIBFDT=y