MIPS: math-emu: Cleanup ieee754si_indef() / ieee754di_indef().

LONG_LONG_MAX is a symbol defined in <limits.h> which may not be available
so better rely on something provided by a kernel header.  While at it,
turn these function-like macros into inline functions.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>