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/uniphier_v7_defconfig b/configs/uniphier_v7_defconfig
index d2a1e3b..47b90d6 100644
--- a/configs/uniphier_v7_defconfig
+++ b/configs/uniphier_v7_defconfig
@@ -54,3 +54,4 @@
 CONFIG_USB_DWC3=y
 CONFIG_USB_DWC3_UNIPHIER=y
 CONFIG_USB_STORAGE=y
+CONFIG_PANIC_HANG=y