clk: iproc: add initial common clock support

This adds basic and generic support for various iProc PLLs and clocks
including the ARMPLL, GENPLL, LCPLL, MIPIPLL, and ASIU clocks.

SoCs under the iProc architecture can define their specific register
offsets and clock parameters for their PLL and clock controllers. These
parameters can be passed as arugments into the generic iProc PLL and
clock setup functions

Derived from code originally provided by Jonathan Richardson
<jonathar@broadcom.com>

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