Documentation: clk: update file names containing referenced structures

Documentation: clk: update file names containing referenced structures

Commit '11f29305e' removes include/linux/clk-private.h and
re-arranges the clock related structures contained in it in
different files. The documentation has not been updated
accordingly, thus it wasn't anymore consistent.

Place the structures referenced by Documentation/clk.txt in the
correct files and update their contents to the latest status.

Signed-off-by: Andi Shyti <andi.shyti@samsung.com>
[geert: Fix path to clk.c, whitespace, more clk_core, ...]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>