drm/i915: Prefer IS_GEN<n> check with bitmask.

Whenever possible we should stick with IS_GEN<n> checks.

Bitmaks has been introduced on commit ae7617f0ef ("drm/i915:
Allow optimized platform checks") for efficiency.

Let's stick with it whenever possible.

This patch was generated with coccinelle:

spatch -sp_file is_gen.cocci *{c,h} --in-place

is_gen.cocci:
@gen2@ expression e; @@
-INTEL_GEN(e) == 2
+IS_GEN2(e)
@gen3@ expression e; @@
-INTEL_GEN(e) == 3
+IS_GEN3(e)
@gen4@ expression e; @@
-INTEL_GEN(e) == 4
+IS_GEN4(e)
@gen5@ expression e; @@
-INTEL_GEN(e) == 5
+IS_GEN5(e)
@gen6@ expression e; @@
-INTEL_GEN(e) == 6
+IS_GEN6(e)
@gen7@ expression e; @@
-INTEL_GEN(e) == 7
+IS_GEN7(e)
@gen8@ expression e; @@
-INTEL_GEN(e) == 8
+IS_GEN8(e)
@gen9@ expression e; @@
-INTEL_GEN(e) == 9
+IS_GEN9(e)
@gen10@ expression e; @@
-INTEL_GEN(e) == 10
+IS_GEN10(e)
@gen11@ expression e; @@
-INTEL_GEN(e) == 11
+IS_GEN11(e)

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181026195143.20353-1-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/intel_psr.c

@@ -574,7 +574,7 @@ static void intel_psr_enable_source(struct intel_dp *intel_dp,
 	if (dev_priv->psr.psr2_enabled) {
 		u32 chicken = I915_READ(CHICKEN_TRANS(cpu_transcoder));
 
-		if (INTEL_GEN(dev_priv) == 9 && !IS_GEMINILAKE(dev_priv))
+		if (IS_GEN9(dev_priv) && !IS_GEMINILAKE(dev_priv))
 			chicken |= (PSR2_VSC_ENABLE_PROG_HEADER
 				   | PSR2_ADD_VERTICAL_LINE_COUNT);