or1k: make the port more generic

Delay slot mach are detected by reading bfd_arch_info.
When a target has delay slot set_gdbarch_single_step_through_delay
has to be initialized.

or1k_cgen_cpu_open is now called with the ENDIAN given by
the bfd_arch_info.

gdb_cgen_cpu_desc has been included in struct gdbarch_tdep.

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