clk: Introduce the clk_hw_get_rate_range function

Some clock providers are hand-crafting their clk_rate_request, and need
to figure out the current boundaries of their clk_hw to fill it
properly.

Let's create such a function for clock providers.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220816112530.1837489-24-maxime@cerno.tech


Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>