clk: Add {devm_}clk_hw_{register,unregister}() APIs

We've largely split the clk consumer and provider APIs along
struct clk and struct clk_hw, but clk_register() still returns a
struct clk pointer for each struct clk_hw that's registered.
Eventually we'd like to only allocate struct clks when there's a
user, because struct clk is per-user now, so clk_register() needs
to change.

Let's add new APIs to register struct clk_hws, but this time
we'll hide the struct clk from the caller by returning an int
error code. Also add an unregistration API that takes the clk_hw
structure that was passed to the registration API. This way
provider drivers never have to deal with a struct clk pointer
unless they're using the clk consumer APIs.

Signed-off-by: Stephen Boyd <[email protected]>

Documentation/driver-model/devres.txt

@@ -236,6 +236,7 @@ certainly invest a bit more effort into libata core layer).
 CLOCK
   devm_clk_get()
   devm_clk_put()
+  devm_clk_hw_register()
 
 DMA
   dmam_alloc_coherent()