payloads/nvramcui: Fix `make clean`

After `make clean` a new build should not be based on stale artifacts.
Hence we have to remove them.

Change-Id: I540a83a6c87b843b1c4c9c55990bf3e91fe90d79
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44180
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

payloads/nvramcui/Makefile

@@ -26,9 +26,9 @@ else
 endif
 
 clean:
-	rm -f nvramcui.elf
+	rm -rf build libpayload nvramcui.elf
 
 distclean: clean
-	rm -rf build libpayload .config .config.old
+	rm -rf .config .config.old
 
 .PHONY: all clean distclean