sandbox: Adjust configuration to hang on panic()

It is annoying to have sandbox enter a boot loop when an assertion
fails. Hang instead, since then the error message is only printed once
and Ctrl-C can be used to quit, as per normal.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index af56571..e96a0d6 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -352,6 +352,7 @@
 CONFIG_FS_CBFS=y
 CONFIG_FS_CRAMFS=y
 CONFIG_ADDR_MAP=y
+CONFIG_PANIC_HANG=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_MBEDTLS_LIB=y
 CONFIG_ECDSA=y