buildsys: add top-level make tidy target

See pve-common's commit 5ae1f2e ("buildsys: add tidy make target")
for details about the chosen xargs parameters.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

Makefile

@@ -16,6 +16,10 @@ DEBS = $(DEB) $(DBG_DEB) $(LIB_DEB)
 
 all: $(DEB) $(DBG_DEB)
 
+.PHONY: tidy
+tidy:
+	git ls-files ':*.p[ml]'| xargs -n4 -P0 proxmox-perltidy
+
 $(BUILDDIR):
 	rm -rf $@ $@.tmp
 	cp -a src $@.tmp