drm/i915: Rename intel_shared_dpll_commit() to _swap_state()

The function intel_shared_dpll_commit() performs the equivalent of
drm_atomic_helper_swap_state() for the shared dpll state, which is not
handled by the helpers. So make it do a full swap of the state and
rename it for consistency.

v2: Fix typo in the commit message. (Durga)
v3: Rebase.
v4: Swap the states instead of just renaming the function. (Daniel)
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Durgadoss R <durgadoss.r@intel.com> (v2)
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v3)
Link: http://patchwork.freedesktop.org/patch/msgid/1483024933-3726-3-git-send-email-ander.conselvan.de.oliveira@intel.com