clk: vt8500: Migrate to clk_hw based registration APIs

Now that we have clk_hw based provider APIs to register clks, we
can get rid of struct clk pointers while registering clks in
these drivers, allowing us to move closer to a clear split of
consumer and provider clk APIs.

Cc: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Cc: Tony Prisk <linux@prisktech.co.nz>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>