MIPS: math-emu: Make NaN classifiers static

The `ieee754sp_isnan' and `ieee754dp_isnan' NaN classifiers are now no
longer externally referred, remove their header prototypes and make them
local to the two only respective places still making use of them.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9693/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/math-emu/ieee754sp.h

@@ -82,6 +82,5 @@ static inline union ieee754sp buildsp(int s, int bx, unsigned m)
 	return r;
 }
 
-extern int ieee754sp_isnan(union ieee754sp);
 extern union ieee754sp __cold ieee754sp_nanxcpt(union ieee754sp);
 extern union ieee754sp ieee754sp_format(int, int, unsigned);