x86: add _ASM_EXTABLE macro to <asm/asm.h>

Instead of open-coding the __ex_table information at each callsite,
construct a common macro that can work regardless of CPU size.
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

include/asm-x86/asm.h

@@ -29,4 +29,11 @@
 
 #endif /* CONFIG_X86_32 */
 
+/* Exception table entry */
+# define _ASM_EXTABLE(from,to) \
+	" .section __ex_table,\"a\"\n" \
+	_ASM_ALIGN "\n" \
+	_ASM_PTR #from "," #to "\n" \
+	" .previous\n"
+
 #endif /* _ASM_X86_ASM_H */