panic: fix incomplete panic log in panic()

Panic log should be printed on the console, but if someone lock the
console when panic, console won't print out panic log.

The incomplete panic log issue will happen in below scenarios:
1. One task call console_lock(), then panic happend before it call
console_unlock(). No panic log can be printed.
2. Cpu 0 call panic()->Cpu 1 call console_lock()->Cpu 0 call
smp_send_stop()
Cpu 1 will be stopped and can't unlock console,only top part of panic log
will be printed.

So unlock console anyway in panic() to keep panic log printed.

Signed-off-by: Qing Zhu <qzhu@marvell.com>