kbuild: clean Modules.symvers in external module dirs
kbuild: clean Modules.symvers in external module dirs

At the moment, running `make clean` in an external module directory does a
nice job of cleaning up with one exception: it leaves behind Modules.symvers.
Attached patch adds this file to the clean list for external modules.

Signed-off-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@gentoo.org>
Signed-off-by: Sam Ravnborg <f16bed56189e249fe4ca8ed10a1ecae60e8ceac0@ravnborg.org>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas