openrisc: support framepointers and STACKTRACE_SUPPORT

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>