m68k: Restore symbol versions for symbols exported from assembly

WARNING: EXPORT symbol "__divsi3" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "__umodsi3" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "__mulsi3" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "__modsi3" [vmlinux] version generation failed, symbol will not be versioned.
WARNING: EXPORT symbol "__udivsi3" [vmlinux] version generation failed, symbol will not be versioned.

Add <asm/asm-prototypes.h> so that genksyms knows the types of these
symbols and can generate CRCs for them.

Fixes: d13ffb56 ("m68k: move exports to definitions"
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[geert: Add warning messages, match actual prototypes in gccint.info]
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>