clk: gate: Add support for specifying parents via DT/pointers

After commit fc0c209c

 ("clk: Allow parents to be specified without
string names") we can use DT or direct clk_hw pointers to specify
parents. Create a generic function that shouldn't be used very often to
encode the multitude of ways of registering a gate clk with different
parent information. Then add a bunch of wrapper macros that only pass
down what needs to be passed down to the generic function to support
this with less arguments.

Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lkml.kernel.org/r/20190830150923.259497-12-sboyd@kernel.org