x86: fix math_emu register frame access

do_device_not_available() is the handler for #NM and it declares that
it takes a unsigned long and calls math_emu(), which takes a long
argument and surprisingly expects the stack frame starting at the zero
argument would match struct math_emu_info, which isn't true regardless
of configuration in the current code.

This patch makes do_device_not_available() take struct pt_regs like
other exception handlers and initialize struct math_emu_info with
pointer to it and pass pointer to the math_emu_info to math_emulate()
like normal C functions do.  This way, unless gcc makes a copy of
struct pt_regs in do_device_not_available(), the register frame is
correctly accessed regardless of kernel configuration or compiler
used.

This doesn't fix all math_emu problems but it at least gets it
somewhat working.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/math-emu/fpu_proto.h

@@ -51,7 +51,7 @@ extern void ffreep(void);
 extern void fst_i_(void);
 extern void fstp_i(void);
 /* fpu_entry.c */
-asmlinkage extern void math_emulate(long arg);
+extern void math_emulate(struct math_emu_info *info);
 extern void math_abort(struct math_emu_info *info, unsigned int signal);
 /* fpu_etc.c */
 extern void FPU_etc(void);