clk: nsp: add clock support for Broadcom Northstar Plus SoC

The Broadcom Northstar Plus SoC is architected under the iProc
architecture. It has the following PLLs: ARMPLL, GENPLL, LCPLL0, all
derived from an onboard crystal.

Signed-off-by: Jon Mason <jonmason@broadcom.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>