Enable SVE2 based assembly kernels when building for SVE2

Sve2 kernels are guarded by -DSVE2, thus needs to be passed during
compilation for them to be included.

Resolves: COMPMID-3891

Signed-off-by: Georgios Pinitas <georgios.pinitas@arm.com>
Change-Id: I8ecb2f2289f2aa5a31958285f56e151019c9b9d6
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/4666
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
diff --git a/SConstruct b/SConstruct
index c2e9a30..15197a6 100644
--- a/SConstruct
+++ b/SConstruct
@@ -205,6 +205,7 @@
 elif 'v8' in env['arch']:
     if 'sve2' in env['arch']:
         env.Append(CXXFLAGS = ['-march=armv8.2-a+sve2+fp16+dotprod'])
+        env.Append(CPPDEFINES = ['SVE2'])
     elif 'sve' in env['arch']:
         env.Append(CXXFLAGS = ['-march=armv8.2-a+sve+fp16+dotprod'])
     elif 'v8.' in env['arch']: