drm/i915/dpll: Rename macro for_each_shared_dpll

Rename the macro for_each_shared_dpll to for_each_dpll since
this loop will not necessarily be used for only shared
dpll in future.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20250515071801.2221120-5-suraj.kandpal@intel.com