lantiq: Allow PKG_ASLR_PIE for DSL and voice drivers

When ASLR_PIE was activated globally these drivers failed to build
because the user space LDFLAGS leaked into the kernel build process.
This was fixed in upstream Linux kernel commit ce99d0bf312d ("kbuild:
clear LDFLAGS in the top Makefile") which went into Linux 4.17. The
lantiq target is now on Linux 4.19 only and these exceptions are not
needed any more.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>