arm64: traps: Add str of description to panic() in die()

arm64: traps: Add str of description to panic() in die()

Currently, there are different description strings in die() such as
die("Oops",,), die("Oops - BUG",,). And panic() called by die() will
always show "Fatal exception" or "Fatal exception in interrupt".

Note that panic() will run any panic handler via panic_notifier_list.
And the string above will be formatted and placed in static buf[]
which will be passed to handler.

So panic handler can not distinguish which Oops it is from the buf if
we want to do some things like reserve the string in memory or panic
statistics. It's not benefit to debug. We need to add more codes to
troubleshoot. Let's utilize existing resource to make debug much simpler.

Signed-off-by: Yue Hu <huyue2@yulong.com>
Link: https://lore.kernel.org/r/20200804085347.10720-1-zbestahu@gmail.com
Signed-off-by: Will Deacon <will@kernel.org>