snow: Turn on CONFIG_PANIC_HELP
snow: Turn on CONFIG_PANIC_HELP

Add this option to make panics easier to decode.

Also put panics in a new stack for snow.

BUG=chrome-os-partner:10146
TEST=manual:
build for all boards
On snow, cause a panic and see that it is reported correctly.

Change-Id: If0b90ec0cec4ccb10041bd12bc21b342581e7f62
Signed-off-by: Simon Glass <c00b0378376498bd9cd974c388df8854c0131d27@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/24506

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