clk: Add stubs for of_clk_*() APIs when CONFIG_OF=n

Compiling the versatile clock driver with COMPILE_TEST=y and CONFIG_OF=n
leads to the following error:

   drivers/clk/versatile/clk-sp810.c: In function 'clk_sp810_of_setup':
   drivers/clk/versatile/clk-sp810.c:103:6: error: implicit declaration of
function 'of_clk_parent_fill' [-Werror=implicit-function-declaration]

Silence it by providing stubs APIs for of_clk_parent_fill().
Throw in a stub for of_clk_get_parent_count() too because we're
in the area.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>