clk: cygnus: add clock support for Broadcom Cygnus

clk: cygnus: add clock support for Broadcom Cygnus

The Broadcom Cygnus SoC is architected under the iProc architecture. It
has the following PLLs: ARMPLL, GENPLL, LCPLL0, MIPIPLL, all dervied
from an onboard crystal. Cygnus also has various ASIU clocks that are
derived directly from the onboard crystal.

Signed-off-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>