tests: Enable Arm64 user defined mem regions test

Signed-off-by: Henry Wang <Henry.Wang@arm.com>

tests/integration.rs

@@ -2277,7 +2277,6 @@ mod tests {
         }
 
         #[test]
-        #[cfg(target_arch = "x86_64")]
         fn test_user_defined_memory_regions() {
             let focal = UbuntuDiskConfig::new(FOCAL_IMAGE_NAME.to_string());
             let guest = Guest::new(Box::new(focal));