Get the gdb/psim emulator functioning again.

aim/machdep.c:

• the RI status register bit needs to be set when doing the mtmsrd 64-bit instruction test
• psim doesn't implement the dcbz instruction so the run-time cacheline test fails. Set the cachline size to 32 to avoid infinite loops in future calls to __syncicache()

aim/platform_chrp.c:

• if after iterating through / and a name property of "cpus" still isn't found, just search directly for '/cpus'.
• psim doesn't put a "reg" property on it's cpu nodes, so assume 0 since it is uniprocessor-only at this point

powerpc/openpic.c

• the number of CPUs reported is 1 too many on psim's openpic

Reviewed by: nwhitehorn
MFC after: 1 week (openpic part)