powerpc: mpc8541: Remove macro CONFIG_MPC8541

Replace CONFIG_MPC8541 with ARCH_MPC8541 in Kconfig and clean up existing
macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/cpu.c b/arch/powerpc/cpu/mpc85xx/cpu.c
index 871935d..c563744 100644
--- a/arch/powerpc/cpu/mpc85xx/cpu.c
+++ b/arch/powerpc/cpu/mpc85xx/cpu.c
@@ -293,7 +293,7 @@
 int do_reset (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 /* Everything after the first generation of PQ3 parts has RSTCR */
-#if defined(CONFIG_ARCH_MPC8540) || defined(CONFIG_MPC8541) || \
+#if defined(CONFIG_ARCH_MPC8540) || defined(CONFIG_ARCH_MPC8541) || \
     defined(CONFIG_MPC8555) || defined(CONFIG_MPC8560)
 	unsigned long val, msr;