Fix GEMV kernels not clamping the output
- The flag is set incorrectly that disables activation function in the GEMV asssembly kernel.
- Test is updated to drive the clamping parameters properly.
- The clamping parameter is set to reduce 20% the dynamic range of the output.
Resolves: KLEIDIAI-545
Signed-off-by: Viet-Hoa Do viet-hoa.do@arm.com