drm/i915: Use POSTING_READ in lcpll code

If we don't use the return value of a mmio read our coding style is to
use the POSTING_READ macro. This avoids cluttering the mmio traces.

While at it add the missing posting read in the lcpll enable function
that Paulo spotted.

v2: Drop the _NOTRACE changes, tracing such wait_for loops in the modeset
code might actually be rather useful!

Cc: Paulo Zanoni <przanoni@gmail.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -6036,13 +6036,14 @@ void hsw_restore_lcpll(struct drm_i915_private *dev_priv)
 	if (val & LCPLL_POWER_DOWN_ALLOW) {
 		val &= ~LCPLL_POWER_DOWN_ALLOW;
 		I915_WRITE(LCPLL_CTL, val);
+		POSTING_READ(LCPLL_CTL);
 	}
 
 	val = I915_READ(D_COMP);
 	val |= D_COMP_COMP_FORCE;
 	val &= ~D_COMP_COMP_DISABLE;
 	I915_WRITE(D_COMP, val);
-	I915_READ(D_COMP);
+	POSTING_READ(D_COMP);
 
 	val = I915_READ(LCPLL_CTL);
 	val &= ~LCPLL_PLL_DISABLE;