m68k: syscalls: switch to generic syscallhdr.sh

Many architectures duplicate similar shell scripts.

This commit converts m68k to use scripts/syscallhdr.sh.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20210301142112.342909-2-masahiroy@kernel.org


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>