or1k.c: registers writeback during single stepping

gpr, npc, ppc and sr registers are now written back
to the cpu, but only when they are changed from
outside of cpu

Signed-off-by: Marek Czerski <ma.czerski@gmail.com>
Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
or1k: fix wrong masking of incoming in_status byte

In some circumstances this can lead to an misinterpreted
unknown status:

Error:  debug IF command write: Unknown status (-1304293920)
Error:  debug IF command write: Unknown status (-1304293920)
Error:  debug IF command write: Unknown status (158502000)

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