drm/i915/hsw, bdw: Add irq_pipe_mask, has_vga power well attributes

The pattern of a power well backing a set of pipe IRQ or VGA
functionality applies to all HSW+ platforms. Using power well attributes
instead of platform checks to decide whether to init/reset pipe IRQs and
VGA correspondingly is cleaner and it allows us to unify the HSW/BDW and
GEN9+ power well code in follow-up patches.

Also use u8 for pipe_mask in related helpers to match the type in the
power well struct.

v2:
- Use u8 instead of u32 for irq_pipe_mask. (Ville)

v3:
- Use u8 for pipe_mask in related helpers too for clarity.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170712155413.29839-1-imre.deak@intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_irq.c

@@ -3038,7 +3038,7 @@ static void gen8_irq_reset(struct drm_device *dev)
 }
 
 void gen8_irq_power_well_post_enable(struct drm_i915_private *dev_priv,
-				     unsigned int pipe_mask)
+				     u8 pipe_mask)
 {
 	uint32_t extra_ier = GEN8_PIPE_VBLANK | GEN8_PIPE_FIFO_UNDERRUN;
 	enum pipe pipe;
@@ -3052,7 +3052,7 @@ void gen8_irq_power_well_post_enable(struct drm_i915_private *dev_priv,
 }
 
 void gen8_irq_power_well_pre_disable(struct drm_i915_private *dev_priv,
-				     unsigned int pipe_mask)
+				     u8 pipe_mask)
 {
 	enum pipe pipe;