powerpc: QEMU_E500: Remove macro CONFIG_QEMU_E500

Replace CONFIG_QEMU_E500 with ARCH_QEMU_E500 in Kconfig and
clean up existing macros.

Signed-off-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/cpu/mpc85xx/Kconfig b/arch/powerpc/cpu/mpc85xx/Kconfig
index acac21e..11ae4ea 100644
--- a/arch/powerpc/cpu/mpc85xx/Kconfig
+++ b/arch/powerpc/cpu/mpc85xx/Kconfig
@@ -186,6 +186,7 @@
 
 config TARGET_QEMU_PPCE500
 	bool "Support qemu-ppce500"
+	select ARCH_QEMU_E500
 	select PHYS_64BIT
 
 config TARGET_T102XQDS
@@ -345,6 +346,9 @@
 config ARCH_P5040
 	bool
 
+config ARCH_QEMU_E500
+	bool
+
 source "board/freescale/b4860qds/Kconfig"
 source "board/freescale/bsc9131rdb/Kconfig"
 source "board/freescale/bsc9132qds/Kconfig"