sparc: fix sparse warning in math_{32,64}

Fix following sparse warning:
math_{32,64}.c: warning: symbol 'do_mathemu' was not declared. Should it be static?

Add prototype in processor_{32,64} and drop extern in traps_{32,64}.c

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>