SCons build system refactoring (phase #2).

* Add kernel selection at build time
* Modify filelist.json to allow files separation
  as part of our kernel decoupling process.

Issues to address after this change will be merged:
   (1) Remove SVE/SVE2 defines from already decoupled kernels
   (2) Adapt the new file list structure (filelist.json)

resolves COMPMID-4996 and COMPMID-5048

Change-Id: I8c17a9d6b150bbc7d8c1f2ed38060be82b6aa904
Signed-off-by: Motti Gondabi <motti.gondabi@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/7006
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: SiCong Li <sicong.li@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/filedefs.json b/filedefs.json
index 0bc030e..76dccff 100644
--- a/filedefs.json
+++ b/filedefs.json
@@ -34,8 +34,7 @@
                 "cxxflags": ["-march=armv8.6-a+sve2+fp16+dotprod"],
                 "cppdefines": ["ARM_COMPUTE_ENABLE_FP16", "ARM_COMPUTE_ENABLE_BF16",
                                "ARM_COMPUTE_ENABLE_I8MM"]
-
             }
         }
     }
-}
+}
\ No newline at end of file