x86/asm: Allow to pass macros to __ASM_FORM()

Use __stringify() at __ASM_FORM() so that user can pass
code including macros to __ASM_FORM().

Signed-off-by: Masami Hiramatsu <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Cc: Juergen Gross <[e-mail]>
Cc: [e-mail]
Cc: Boris Ostrovsky <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Stefano Stabellini <[e-mail]>
Cc: Andrew Cooper <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: [e-mail]
Cc: Randy Dunlap <[e-mail]>
Cc: Josh Poimboeuf <[e-mail]>
Link: https://lkml.kernel.org/r/156777562873.25081.2288083344657460959.stgit@devnote2

arch/x86/include/asm/asm.h

···
 # define __ASM_FORM_RAW(x)     x
 # define __ASM_FORM_COMMA(x) x,
 #else
-# define __ASM_FORM(x)	" " #x " "
-# define __ASM_FORM_RAW(x)     #x
-# define __ASM_FORM_COMMA(x) " " #x ","
+#include <linux/stringify.h>
+
+# define __ASM_FORM(x)	" " __stringify(x) " "
+# define __ASM_FORM_RAW(x)     __stringify(x)
+# define __ASM_FORM_COMMA(x) " " __stringify(x) ","
 #endif
 
 #ifndef __x86_64__