powerpc: define FUNC_START/FUNC_END

gcc provides FUNC_START/FUNC_END macros to help with creating
assembly functions. Mirror these in the kernel so we can more easily
share code between userspace and the kernel. FUNC_END is just a
stub since we don't currently annotate the end of kernel functions.

It might make sense to do a wholesale search and replace, but for
now just create a couple of defines.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

arch/powerpc/include/asm/ppc_asm.h

@@ -286,6 +286,9 @@ GLUE(.,name):
 
 #endif
 
+#define FUNC_START(name)	_GLOBAL(name)
+#define FUNC_END(name)
+
 /* 
  * LOAD_REG_IMMEDIATE(rn, expr)
  *   Loads the value of the constant expression 'expr' into register 'rn'