avr32: setup crt for early panic()

Before the CRT was (fully) set up in kernel_entry (bss cleared before in
_start, but also not before jump to panic() in no_tag_table case).

This patch fixes this up to have a fully working CRT when branching to panic()
in no_tag_table.

Signed-off-by: Andreas Bießmann <andreas@biessmann.de>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Cc: stable@vger.kernel.org