powerpc: convert to setup_initial_init_mm()

Use setup_initial_init_mm() helper to simplify code.

Link: https://lkml.kernel.org/r/20210608083418.137226-12-wangkefeng.wang@huawei.comSigned-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/powerpc/kernel/setup-common.c

@@ -926,10 +926,7 @@ void __init setup_arch(char **cmdline_p)
 
 	klp_init_thread_info(&init_task);
 
-	init_mm.start_code = (unsigned long)_stext;
-	init_mm.end_code = (unsigned long) _etext;
-	init_mm.end_data = (unsigned long) _edata;
-	init_mm.brk = (unsigned long)_end;
+	setup_initial_init_mm(_stext, _etext, _edata, _end);
 
 	mm_iommu_init(&init_mm);
 	irqstack_early_init();