drm/i915/dpll: Rename intel_dpll

Rename intel_dpll to intel_dpll_global so that intel_shared_dpll
can be renamed to intel_dpll in an effort to move away from the shared
naming convention.
Also intel_dpll according to it's comment tracks global dpll rather
than individual hence making more sense this gets changed.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20250515071801.2221120-2-suraj.kandpal@intel.com