Move i386/isa/npx.c to i386i386/npx.c.

The i386 FPU (AKA npx) code does not depend on ISA devices at all,
after the support for IRQ13 FPU exceptions was removed.  Put the file
into the expected place in the kernel source tree.

Discussed with:	jhb
Sponsored by:	The FreeBSD Foundation

sys/conf/files.i386

@@ -489,6 +489,7 @@ i386/i386/minidump_machdep.c	standard
 i386/i386/mp_clock.c		optional smp
 i386/i386/mp_machdep.c		optional smp
 i386/i386/mpboot.s		optional smp
+i386/i386/npx.c			standard
 i386/i386/perfmon.c		optional perfmon
 i386/i386/pmap.c		standard
 i386/i386/ptrace_machdep.c	standard
@@ -519,7 +520,6 @@ i386/ibcs2/ibcs2_xenix.c	optional ibcs2
 i386/ibcs2/ibcs2_xenix_sysent.c	optional ibcs2
 i386/ibcs2/imgact_coff.c	optional ibcs2
 i386/isa/elink.c		optional ep
-i386/isa/npx.c			standard
 i386/isa/pmtimer.c		optional pmtimer
 i386/isa/prof_machdep.c		optional profiling-routine
 i386/linux/imgact_linux.c	optional compat_linux