msm: clock: Move parent field into top level struct clk

Maintaining a parent field inside each clock type leads to pointless
repetition of code. Almost all clocks have parents, so move the parent
field to top level struct clk, have it updated whenever the parent changes
for a clock and remove the get_parent ops implementation.

Change-Id: Id897a55d496446a1047322d40d8df041dfea5840
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>