drivers/intel/gma: Allow SPARK function with side effects

Explicitly specifying the aspect `Side_Effects' is necessary for GCC
toolchains from 14.0 on. As older toolchains don't know the aspect,
we have to silence a warning about it, though.

Change-Id: I1eb879f57437587dc11d879fcc4042a70d384786
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80616
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Reviewed-by: Thomas Heijligen <src@posteo.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/gnat.adc b/gnat.adc
index 5a03406..5ebc91b 100644
--- a/gnat.adc
+++ b/gnat.adc
@@ -28,3 +28,7 @@
    Refined_Post         => Disable);
 pragma Overflow_Mode (General => Strict, Assertions => Eliminated);
 pragma SPARK_Mode (On);
+
+pragma Warnings
+  (GNAT, Off, """Side_Effects"" is not a valid aspect identifier",
+   Reason => """Side_Effects"" is new and needed for toolchain transition.");