[POWERPC] Revise PPC44x MMU code for arch/powerpc

This patch takes the definitions for the PPC44x MMU (a software loaded
TLB) from asm-ppc/mmu.h, cleans them up of things no longer necessary
in arch/powerpc and puts them in a new asm-powerpc/mmu_44x.h file.  It
also substantially simplifies arch/powerpc/mm/44x_mmu.c and makes a
couple of small fixes necessary for the 44x MMU code to build and work
properly in arch/powerpc.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/head_44x.S

@@ -120,8 +120,8 @@ skpinv:	addi	r4,r4,1				/* Increment */
  * Configure and load pinned entry into TLB slot 63.
  */
 
-	lis	r3,KERNELBASE@h		/* Load the kernel virtual address */
-	ori	r3,r3,KERNELBASE@l
+	lis	r3,PAGE_OFFSET@h
+	ori	r3,r3,PAGE_OFFSET@l
 
 	/* Kernel is at the base of RAM */
 	li r4, 0			/* Load the kernel physical address */