zephyr/Kconfig: allow xip-revert only for xip-mode

BOOT_DIRECT_XIP_REVER enable code which shall only be enabled
while BOOT_DIRECT_XIP=y.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index 1386f5e..e08ea74 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -227,6 +227,7 @@
 
 config BOOT_DIRECT_XIP_REVERT
 	bool "Enable the revert mechanism in direct-xip mode"
+	depends on BOOT_DIRECT_XIP
 	default n
 	help
 	  If y, enables the revert mechanism in direct-xip similar to the one in