clk: Move __clk_{get,put}() into private clk.h API

We can move these APIs into the private header file now that we
don't have any users of the __clk_get() and __clk_put() APIs
outside of clkdev.c and clk.c.

Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>