gdb/target: add or1k target

Adds GDB or1k-tdep files. Those files are copied from opencores
GDB 7.2 repo with a small adjustment.

or32_single_step_through_delay as been modified to use cgen_lookup_insn
to decode the fetched instruction.

I think there should be a test here to check for the delay slot support.
When there is no delay slot, we should always return 0.

For now, couldn't find a good way to test this...

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>