powerpc: Fix up elf_read_implies_exec() usage

We believe if a toolchain supports PT_GNU_STACK that it sets the proper
PHDR permissions.  Therefor elf_read_implies_exec() should only be true
if we don't see PT_GNU_STACK set.
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/elf.h

@@ -256,11 +256,11 @@ do {								\
  * even if we have an executable stack.
  */
 # define elf_read_implies_exec(ex, exec_stk) (test_thread_flag(TIF_32BIT) ? \
-		(exec_stk != EXSTACK_DISABLE_X) : 0)
+		(exec_stk == EXSTACK_DEFAULT) : 0)
 #else 
 # define SET_PERSONALITY(ex) \
   set_personality(PER_LINUX | (current->personality & (~PER_MASK)))
-# define elf_read_implies_exec(ex, exec_stk) (exec_stk != EXSTACK_DISABLE_X)
+# define elf_read_implies_exec(ex, exec_stk) (exec_stk == EXSTACK_DEFAULT)
 #endif /* __powerpc64__ */
 
 extern int dcache_bsize;