generic: fix warning orphan section from module exports in aarch64

generic: fix warning orphan section from module exports in aarch64

kernel linux now have 2 different export.h include, one from
linux/export.h and one from asm-generic/export.h

While most of our target user linux/export.h, aarch64 based target use
asm-generic/export.h that is not patched with the changes of
221-module_exports.

Patch also this additional header to fix multiple

aarch64-openwrt-linux-musl-ld: warning: orphan section `__ksymtab_strings' from `arch/arm64/kernel/head.o' being placed in section `__ksymtab_strings'

warning during kernel compilation.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>