drm/i915: Refactor platform specifics out of intel_get_shared_dpll()

The function intel_get_shared_dpll() had a more or less generic
implementation with some platform specific checks to handle smaller
differences between platforms. However, the minimalist approach forces
bigger differences between platforms to be implemented outside of the
shared dpll code (see the *_ddi_pll_select() functions in intel_ddi.c,
for instance).

This patch changes the implementation of intel_get_share_dpll() so that
a completely platform specific version can be used, providing helpers to
reduce code duplication. This should allow the code from the ddi pll
select functions to be moved, and also make room for making more dplls
managed by the shared dpll infrastructure.

v2: WARN_ON(!dpll_mgr) in intel_get_shared_dpll(). (Maarten)
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1457451987-17466-9-git-send-email-ander.conselvan.de.oliveira@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1810,6 +1810,7 @@ struct drm_i915_private {
 	/* dpll and cdclk state is protected by connection_mutex */
 	int num_shared_dpll;
 	struct intel_shared_dpll shared_dplls[I915_NUM_PLLS];
+	const struct intel_dpll_mgr *dpll_mgr;
 
 	unsigned int active_crtcs;
 	unsigned int min_pixclk[I915_MAX_PIPES];

drivers/gpu/drm/i915/intel_dpll_mgr.h

@@ -30,6 +30,8 @@ struct intel_crtc;
 struct intel_crtc_state;
 struct intel_shared_dpll;
 
+struct intel_dpll_mgr;
+
 enum intel_dpll_id {
 	DPLL_ID_PRIVATE = -1, /* non-shared dpll in use */
 	/* real shared dpll ids must be >= 0 */