msm: clock-8960: Chain dependencies between vcodec AXI clocks

Don't require drivers to explicitly enable/disable vcodec_clk,
vcodec_axi_a_clk and vcodec_axi_b_clk since, in practice, all
three are always needed at the same time.

Create a dependency chain for these clocks so that enabling
vcodec_clk enables all the rest.  The chain looks like:

vcodec_clk->vcodec_axi_clk->vcodec_axi_a_clk->vcodec_axi_b_clk

Signed-off-by: Matt Wagantall <mattw@codeaurora.org>