For lockdep support a reliable stack trace mechanism is needed.  This
patch adds support in OpenRISC for the stacktrace framework, implemented
by a simple unwinder api.  The unwinder api supports both framepointer
and basic stack tracing.

The unwinder is now used to replace the stack_dump() implementation as
well. The new traces are inline with other architectures trace format:

 Call trace:
 [<c0004448>] show_stack+0x3c/0x58
 [<c031c940>] dump_stack+0xa8/0xe4
 [<c0008104>] __cpu_up+0x64/0x130
 [<c000d268>] bringup_cpu+0x3c/0x178
 [<c000d038>] cpuhp_invoke_callback+0xa8/0x1fc
 [<c000d680>] cpuhp_up_callbacks+0x44/0x14c
 [<c000e400>] cpu_up+0x14c/0x1bc
 [<c041da60>] smp_init+0x104/0x15c
 [<c033843c>] ? kernel_init+0x0/0x140
 [<c0415e04>] kernel_init_freeable+0xbc/0x25c
 [<c033843c>] ? kernel_init+0x0/0x140
 [<c0338458>] kernel_init+0x1c/0x140
 [<c003a174>] ? schedule_tail+0x18/0xa0
 [<c0006b80>] ret_from_fork+0x1c/0x9c
Signed-off-by: Stafford Horne <shorne@gmail.com>