clk: ti: dpll: convert DPLL support code to use clk_hw instead of clk ptrs

Convert DPLL support code to use clk_hw pointers for reference and bypass
clocks. This allows us to use clk_hw_* APIs for accessing any required
parameters for these clocks, avoiding some locking problems at least with
DPLL enable code; this used clk_get_rate which uses mutex but isn't
good under clk_enable / clk_disable.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>