clk: exynos: Don't expose prototypes for not used functions

clk: exynos: Don't expose prototypes for not used functions

Samsung CCF is meant to be used from the clock drivers by calling the
CMU registration API, i.e.:
  - samsung_cmu_register_one() -- for top-level CMU
  - samsung_register_cmu() -- for the rest of CMUs

Functions for registering separate clocks is probably not going to be
very useful, and isn't used at the moment. Remove prototypes of those
functions to make the Samsung CCF interface more compact and clear.

No functional change.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>