clk: qcom: clock-debug-8994: Change debug clocks to use orphan list

Some debug mux parents might not be ready until the clock driver
providing it becomes ready. Use orphan list support to handle external
debug clocks, instead of failing the probe of clock_debug controller.

In addition, move external debug clock registration from
clock-gcc-8994 to clock-debug-8994.

Change-Id: I764d1fd3cab1af878bd567e30e02d62143204711
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>