pps: Avoid duplicate elements in with_datasources array.

Setting -Dperfetto=true and -Ddatasources=intel,panfrost to the
meson command line resulted in duplicate elements.

Fixes: 92180a4376 ("pps: Intel pps driver")
Fixes: 513d1baaea ("pps: Panfrost pps driver")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12379>

src/intel/ds/meson.build

@@ -27,4 +27,6 @@ pps_intel_dep = declare_dependency(
 )
 
 pps_datasources += pps_intel_dep
-with_datasources += 'intel'
+if not with_datasources.contains('intel')
+  with_datasources += 'intel'
+endif

src/panfrost/ds/meson.build

@@ -28,4 +28,6 @@ pps_panfrost_dep = declare_dependency(
 )
 
 pps_datasources += pps_panfrost_dep
-with_datasources += 'panfrost'
+if not with_datasources.contains('panfrost')
+  with_datasources += 'panfrost'
+endif