Emulate a few more instructions in software - especially useful during
singlestepping (xmon/kprobes).

Instructions emulated with this patch are mfcr/mtcr rX, mfxer/mtxer rX,
mflr/mtlr rX, mfctr/mtctr rX and mr rA,rB.
Signed-off-by: NAnanth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>