always enable regparm on i386

The patch below always enables regparm on i386 (with gcc >= 3.0).

With this patch, it should get a better testing coverage in -mm.

This patch should help to find bugs that show up with regparm enabled.

@@ -877,9 +877,8 @@
 	default y
 
 config REGPARM
-	bool "Use register arguments (EXPERIMENTAL)"
-	depends on EXPERIMENTAL
-	default n
+	bool
+	default y
 	help
 	Compile the kernel with -mregparm=3. This uses an different ABI
 	and passes the first three arguments of a function call in registers.

I'd prefer to keep the config option so that people can diagnose compiler and kernel bugs by disabling it. This has proved useful in the past.