ARM: w90x900: normalize clk API

w90x900 still provides its own variant of the clk API rather than using
the generic COMMON_CLK API. This generally works, but it causes some link
errors with drivers using the clk_set_rate, clk_get_parent, clk_set_parent
or clk_round_rate functions when a platform lacks those interfaces.

This adds empty stub implementations for each of them, and I don't even
try to do something useful here but instead just print a WARN() message
to make it obvious what is going on if they ever end up being called.

The drivers that call these won't be used on these platforms (otherwise
we'd get a link error today), so the added code is harmless bloat and
will warn about accidental use.

A while ago there was a proposal to change w90x900 to use the common-clk
implementation, which would be the way it should be handled properly.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>