Don't create native bridge variants of vendor modules

The logic in cc.Module.ImageMutatorBegin() to skip creating vendor
variants for native bridge modules stopped working when the image
mutator was moved before the arch mutator because the native
bridge variant hadn't been created yet.  Move the logic to the arch
mutator to avoid creating native bridge variants for vendor variants.

Fixes: 146486214
Test: lunch aosp_cf_x86_pasan-userdebug && m SANITIZE_TARGET=address
Change-Id: I46cff4905f929c9989d005f0ceb01388d47323c1