microblaze: Stack trace support

This is working implemetation but the problem is that
Microblaze misses frame pointer that's why is there
big loop which trace and show all addresses which are in text.
It shows addresses which are in registers, etc.

This is problem and this is the reason why all Microblaze
traces are wrong. There is an option to do hacks and trace
the kernel code but this is too complicated.

Signed-off-by: Michal Simek <monstr@monstr.eu>