drm/i915/dpll: Rename intel_dpll_funcs

Rename intel_dpll_funcs to intel_dpll_global_funcs so that later
on intel_shared_dpll_funcs can be renamed to intel_dpll_funcs.
This is done to move away from the shared naming convention since
starting MTL dpll's are not shared among PHYs.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20250515071801.2221120-3-suraj.kandpal@intel.com