Move CONFIG_PANIC_HANG to Kconfig

Freescale (NXP) boards have lots of defconfig files per board.
I used "imply PANIC_HANG" for them.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: York Sun <york.sun@nxp.com>
diff --git a/configs/qemu-ppce500_defconfig b/configs/qemu-ppce500_defconfig
index f1db0d0..9d27755 100644
--- a/configs/qemu-ppce500_defconfig
+++ b/configs/qemu-ppce500_defconfig
@@ -24,4 +24,5 @@
 CONFIG_NETDEVICES=y
 CONFIG_E1000=y
 CONFIG_SYS_NS16550=y
+CONFIG_PANIC_HANG=y
 CONFIG_OF_LIBFDT=y