MIPS: BMIPS: Add PRId for BMIPS5200 (Whirlwind)

This is a dual core (quad thread) BMIPS5000.  It needs a little extra
code to boot the second core (CPU2/CPU3), but for now we can treat it the
same as a single core BMIPS5000.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: f.fainelli@gmail.com
Cc: mbizon@freebox.fr
Cc: jogo@openwrt.org
Cc: jfraser@broadcom.com
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8166/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>