powerpc: Endian safe trampoline

Create a trampoline that works in either endian and flips to
the expected endian. Use it for primary and secondary thread
entry as well as RTAS and OF call return.

Credit for finding the magic instruction goes to Paul Mackerras

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/head_64.S

@@ -68,6 +68,7 @@ _stext:
 _GLOBAL(__start)
 	/* NOP this out unconditionally */
 BEGIN_FTR_SECTION
+	FIXUP_ENDIAN
 	b	.__start_initialization_multiplatform
 END_FTR_SECTION(0, 1)
 
@@ -115,6 +116,7 @@ __run_at_load:
  */
 	.globl	__secondary_hold
 __secondary_hold:
+	FIXUP_ENDIAN
 #ifndef CONFIG_PPC_BOOK3E
 	mfmsr	r24
 	ori	r24,r24,MSR_RI
@@ -205,6 +207,7 @@ _GLOBAL(generic_secondary_thread_init)
  * as SCOM before entry).
  */
 _GLOBAL(generic_secondary_smp_init)
+	FIXUP_ENDIAN
 	mr	r24,r3
 	mr	r25,r4