m68k: math-emu: Replace external declarations by header inclusion

m68k: math-emu: Replace external declarations by header inclusion

Replace the (incorrect) external declarations by an inclusion of the
appropriate header file.

Semantically, the "src" parameters of the various fp_*() functions are
constant.  However, they cannot actually be const as most of these
functions perform a normalization step first.  As the fp_one constant
passed to fp_add() is already normalized, it is safe to cast away its
constness when making the function call.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/163bc2f64b5a3dd7b96a12aaca6733b408ddc880.1692283195.git.geert@linux-m68k.org