[POWERPC] Add a sd command (spu dump) to xmon to dump spu local store

Add a command to xmon to dump the memory of a spu's local store.
This mimics the 'd' command which dumps regular memory, but does
a little hand holding by taking the user supplied address and
finding that offset in the local store for the specified spu.

This makes it easy for example to look at what was executing on a spu:

1:mon> ss
...
Stopped spu 04 (was running)
...
1:mon> sf 4
Dumping spu fields at address c0000000019e0a00:
...
  problem->spu_npc_RW     = 0x228
...
1:mon> sd 4 0x228
d000080080318228 01a00c021cffc408 4020007f217ff488  |........@ ..!...|

Aha, 01a00c02, which is of course rdch $2,$ch24 !

--

Updated to only do the setjmp goo around the spu access, and not
around prdump because it does its own (via mread).

Also the num variable is now common between sf and sd, so you don't
have to keep typing the spu number in if you're repeating commands
on the same spu.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>