kconfig: Add -MP option so .d files include empty targets

Prevents make-level errors when switching IDF versions, as headers may be removed.

Similar to some mentioned here:
https://github.com/espressif/esp-idf/issues/712

tools/kconfig/Makefile

@@ -165,7 +165,7 @@ check-lxdialog  := $(SRCDIR)/lxdialog/check-lxdialog.sh
 # Use recursively expanded variables so we do not call gcc unless
 # we really need to do so. (Do not call gcc as part of make mrproper)
 CFLAGS += $(shell $(CONFIG_SHELL) $(check-lxdialog) -ccflags) \
-                    -DLOCALE -MMD
+                    -DLOCALE -MMD -MP
 
 %.o: $(SRCDIR)/%.c
 	$(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@