[POWERPC] 8xx: Set initial memory limit.

The 8xx can only support a max of 8M during early boot (it seems a lot of
8xx boards only have 8M so the bug was never triggered), but the early
allocator isn't aware of this.  The following change makes it able to run
with larger memory.
Signed-off-by: NJohn Traill <john.traill@freescale.com>
Signed-off-by: NVitaly Bordug <vitb@kernel.crashing.org>
Signed-off-by: NScott Wood <scottwood@freescale.com>
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>

arch/powerpc/mm/init_32.c

@@ -132,6 +132,9 @@ void __init MMU_init(void)
 	/* 601 can only access 16MB at the moment */
 	if (PVR_VER(mfspr(SPRN_PVR)) == 1)
 		__initial_memory_limit = 0x01000000;
+	/* 8xx can only access 8MB at the moment */
+	if (PVR_VER(mfspr(SPRN_PVR)) == 0x50)
+		__initial_memory_limit = 0x00800000;
 
 	/* parse args from command line */
 	MMU_setup();