mpc83xx: Introduce ARCH_MPC837X

Replace CONFIG_MPC837x with a proper CONFIG_ARCH_MPC837X Kconfig option.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/arch/powerpc/cpu/mpc83xx/Kconfig b/arch/powerpc/cpu/mpc83xx/Kconfig
index 5f9d036..e41f4d1 100644
--- a/arch/powerpc/cpu/mpc83xx/Kconfig
+++ b/arch/powerpc/cpu/mpc83xx/Kconfig
@@ -64,12 +64,14 @@
 
 config TARGET_MPC837XEMDS
 	bool "Support MPC837XEMDS"
+	select ARCH_MPC837X
 	select BOARD_EARLY_INIT_F
 	imply CMD_SATA
 	imply FSL_SATA
 
 config TARGET_MPC837XERDB
 	bool "Support MPC837XERDB"
+	select ARCH_MPC837X
 	select BOARD_EARLY_INIT_F
 
 config TARGET_IDS8313
@@ -151,6 +153,9 @@
 config ARCH_MPC8360
 	bool
 
+config ARCH_MPC837X
+	bool
+
 source "board/esd/vme8349/Kconfig"
 source "board/freescale/mpc8308rdb/Kconfig"
 source "board/freescale/mpc8313erdb/Kconfig"