MIPS: Netlogic: Update XLP9XX/2XX core freq calculation

Calculate XLP 9XX and 2XX core frequency from the per-core PLL. This
should give the correct value for all board configurations.

Signed-off-by: Jayachandran C <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6870/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>