clk: add BCM63XX gated clock controller driver

Add a driver for the gated clock controller found on MIPS based BCM63XX
SoCs.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
[sboyd@kernel.org: Remove module.h include and associated things for a
non-modular driver, add static on data tables, drop of_match_ptr()
usage, fix spdx tag to be a C++ style comment]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>