powerpc: EX_TABLE macro for exception tables

This macro is taken from s390, and allows more flexibility in
changing exception table format.

mpe: Put it in ppc_asm.h and only define one version using
stringinfy_in_c(). Add some empty definitions and headers to keep the
selftests happy.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/fsl_rio.c

@@ -80,10 +80,8 @@
 		"3:	li %1,-1\n"			\
 		"	li %0,%3\n"			\
 		"	b 2b\n"				\
-		".section __ex_table,\"a\"\n"		\
-			PPC_LONG_ALIGN "\n"		\
-			PPC_LONG "1b,3b\n"		\
-		".text"					\
+		".previous\n"				\
+		EX_TABLE(1b, 3b)			\
 		: "=r" (err), "=r" (x)			\
 		: "b" (addr), "i" (-EFAULT), "0" (err))