[scons multi_isa] extend multi_isa build to support armv8-a march

This change adds support for multi isa build with armv8-a as the
base micro architecture. To enable this, use 'arch=armv8a' and 'multi_isa=1'
build flags during scons build. This build option doesn't include
fp16 vector arithmetic. To include fp16 vector arithmetic, use 'arch=armv8.2-a'
and 'multi_isa=1' build option.

Signed-off-by: Sunita Nadampalli <nadampal@amazon.com>
Change-Id: Ib5ca61dc65603382baee53b3ec30b2b817beda3c
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/9474
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: SiCong Li <sicong.li@arm.com>
Reviewed-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>
diff --git a/filedefs.json b/filedefs.json
index 3422eeb..8ffa3d9 100644
--- a/filedefs.json
+++ b/filedefs.json
@@ -2,7 +2,7 @@
     "cpu": {
         "arch" : {
             "armv8-a": {
-                "cxxflags": ["-march=armv8.2-a"]
+                "cxxflags": ["-march=armv8-a"]
             },
             "armv8.2-a": {
                 "cxxflags": ["-march=armv8.2-a+fp16"],