target-ppc: fixed translation of mcrxr instruction

Fixed bug in gen_mcrxr() in target-ppc/translate.c:
The XER[SO], XER[OV], and XER[CA] flags are stored in the least
significant bit (bit 0) of their respective registers. They need
to be shifted left (by their respective offsets) to generate the final
XER value. The old translation code for the 'mcrxr' instruction
was assuming that  the flags are stored in bit 2, and was shifting them
right (incorrectly)

Signed-off-by: Sorav Bansal <sbansal@cse.iitd.ernet.in>
Reviewed-by: Tom Musta <tommusta@gmail.com>
Tested-by: Tom Musta <tommusta@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>