drm/i915/dpll: Rename intel_shared_dpll_state

Rename intel_shared_dpll_state to just intel_dpll_state since it may
not necessarily store share dpll state info specially since
DISPLAY_VER >= 14 PLL's are not shared.
Also change the name of variables which may have been associated as
a shared_dpll.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://lore.kernel.org/r/20250515071801.2221120-4-suraj.kandpal@intel.com