clk: clk-gpio: Make GPIO clock provider use descriptors only

After som grep:ing it turns out nothing in the kernel is really calling
clk_[hw_]_register_gpio_[gate|mux](). All existing instances are just
created directly from the device tree probe functions at the bottom of
the clk-gpio.c clock provider file.

This means we can change the signature of the function without any
consequences! Everyone should be using GPIO descriptors now, so let's
just go in and enforce that.

This saves a bit of code since GPIO descriptors know inherently if they
are active low so no need for the code keeping track of that.

We leave it to the caller to come up with the GPIO descriptor. It is
nowadays possible to do that even without a corresponding device, so
no excuse not to pass them around. The one in-kernel user lifecycles
it using devm_gpiod_get() in gpio_clk_driver_probe().

Cc: Sergej Sawazki <ce3a@gmx.de>
Cc: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>