mpc83xx: Migrate CONFIG_SYS_IMMR to Kconfig

Migrate CONFIG_SYS_IMMR to Kconfig for MPC83xx.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
diff --git a/configs/ids8313_defconfig b/configs/ids8313_defconfig
index 24590d1..9c16a12 100644
--- a/configs/ids8313_defconfig
+++ b/configs/ids8313_defconfig
@@ -4,6 +4,7 @@
 CONFIG_MPC83xx=y
 CONFIG_HIGH_BATS=y
 CONFIG_TARGET_IDS8313=y
+CONFIG_SYS_IMMR=0xF0000000
 CONFIG_CORE_PLL_RATIO_2_1=y
 CONFIG_PCI_HOST_MODE_ENABLE=y
 CONFIG_BOOT_ROM_INTERFACE_GPCM_8BIT=y