kselftest/arm64: Cover disabling streaming mode without SVE in fp-ptrace

kselftest/arm64: Cover disabling streaming mode without SVE in fp-ptrace

On a system which support SME but not SVE we can now disable streaming mode
via ptrace by writing FPSIMD formatted data through NT_ARM_SVE with a VL of
0. Extend fp-ptrace to cover rather than skip these cases, relax the check
for SVE writes of FPSIMD format data to not skip if SME is supported and
accept 0 as the VL when performing the ptrace write.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>