CLK: TI: DPLL: simplify autoidle register detection logic

AMxxxx dpll_data previously had autoidle_mask set, even if these SoC:s
don't have autoidle register. Remove the bit-field value as it is unused,
also drop the unnecessary DPLL_HAS_AUTOIDLE flag passing during init,
as we can just simply check against the contents of the autoidle_mask.

Signed-off-by: Tero Kristo <t-kristo@ti.com>