[POWERPC] Fix modpost warnings from head*.S on ppc32

We get warnings like the following from the various ppc32 head*.S files:

WARNING: vmlinux.o(.text+0x358): Section mismatch: reference to .init.text:early_init (between 'skpinv' and 'interrupt_base')
WARNING: vmlinux.o(.text+0x380): Section mismatch: reference to .init.text:machine_init (between 'skpinv' and 'interrupt_base')
WARNING: vmlinux.o(.text+0x384): Section mismatch: reference to .init.text:MMU_init (between 'skpinv' and 'interrupt_base')
WARNING: vmlinux.o(.text+0x3aa): Section mismatch: reference to .init.text:start_kernel (between 'skpinv' and 'interrupt_base')
WARNING: vmlinux.o(.text+0x3ae): Section mismatch: reference to .init.text:start_kernel (between 'skpinv' and 'interrupt_base')

Added a .text.head section simliar to what other architectures do since
modpost already excludes this from its warnings.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index a8e0457..00bdb6d 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S
@@ -52,9 +52,9 @@
  *
  * This is all going to change RSN when we add bi_recs.......  -- Dan
  */
-	.text
-_GLOBAL(_stext)
-_GLOBAL(_start)
+	.section	.text.head, "ax"
+_ENTRY(_stext);
+_ENTRY(_start);
 
 	/* Save parameters we are passed.
 	*/
@@ -89,9 +89,9 @@
  */
 	. = 0xc0
 crit_save:
-_GLOBAL(crit_r10)
+_ENTRY(crit_r10)
 	.space	4
-_GLOBAL(crit_r11)
+_ENTRY(crit_r11)
 	.space	4
 
 /*
@@ -814,7 +814,7 @@
  * The PowerPC 4xx family of processors do not have an FPU, so this just
  * returns.
  */
-_GLOBAL(giveup_fpu)
+_ENTRY(giveup_fpu)
 	blr
 
 /* This is where the main kernel code starts.