clk: introduce enable_count

As what Linux Kernel 5.3.0 provides when enable/disable clk,
there is an enable_count in clk_core_disable/enable. Introduce
enable_count to track the clk enable/disable count when
clk_enable/disable for CCF. And Initialize enable_count to 0 when
register the clk.

And clk tree dump with enable_count will be supported, it will
be easy for us to check the clk status with enable_count

Signed-off-by: Peng Fan <peng.fan@nxp.com>