MIPS: Netlogic: PIC freq calculation for XLP 9XX/2XX

Update PIC frequency calculation for XLP9XX and 2XX processors using
the correct PLL registers. This should work for all possible board
configurations.

Signed-off-by: Ganesan Ramalingam <ganesanr@broadcom.com>
Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6876/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>