clk: ns2: add clock support for Broadcom Northstar 2 SoC

The Broadcom Northstar 2 SoC is architected under the iProc
architecture. It has the following PLLs: GENPLL SCR, GENPLL SW,
LCPLL DDR, LCPLL Ports, all derived from an onboard crystal.

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