MIPS: BMIPS: BMIPS4380 and BMIPS5000 support RIXI

MIPS: BMIPS: BMIPS4380 and BMIPS5000 support RIXI

Make BMIPS4380 and BMIPS5000 advertise support for RIXI through
cpu_probe_broadcom(). bmips_cpu_setup() needs to be called shortly after that,
during prom_init() in order to enable the proper Broadcom-specific register to
turn on RIXI and the "rotr" instruction.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Cc: john@phrozen.org
Cc: cernekee@gmail.com
Cc: jon.fraser@broadcom.com
Cc: pgynther@google.com
Cc: paul.burton@imgtec.com
Cc: ddaney.cavm@gmail.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12507/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>