python3: Let distro configure if pycs are included

We want to remove python cached files in ramdisk images to reduce their
size, but keep them in mmc images to have better performances.

We therefor need to make this configurable from distro config.

BugzID: 67738

recipes-devtools/python/python3_%.bbappend

@@ -1,8 +1,6 @@
 EXTRA_OECONF_remove = "ac_cv_header_bluetooth_bluetooth_h=no ac_cv_header_bluetooth_h=no"
 
-INCLUDE_PYCS = "0"
-
-PACKAGE_PREPROCESS_FUNCS += "clean_pycache"
+PACKAGE_PREPROCESS_FUNCS += "${@ 'clean_pycache' if not bb.utils.to_boolean(d.getVar('INCLUDE_PYCS')) else '' }"
 
 clean_pycache(){
     find ${PKGD} | grep -E "(__pycache__|\.pyc|\.pyo$)" | xargs rm -rf