x86: Change is_ISA_range() into an inline function

Change is_ISA_range() from a macro to an inline function.  This makes
it type safe, and also allows it to be assigned to a function pointer
if necessary.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091119202341.GA4420@sgi.com>