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>

Author: broonie

tools/testing/selftests/arm64/fp/fp-ptrace.c

@@ -1071,7 +1071,7 @@ static bool sve_write_supported(struct test_config *config)
 
 static bool sve_write_fpsimd_supported(struct test_config *config)
 {
-	if (!sve_supported())
+	if (!sve_supported() && !sme_supported())
 		return false;
 
 	if ((config->svcr_in & SVCR_ZA) != (config->svcr_expected & SVCR_ZA))
@@ -1231,9 +1231,6 @@ static void sve_write_fpsimd(pid_t child, struct test_config *config)
 	vl = vl_expected(config);
 	vq = __sve_vq_from_vl(vl);
 
-	if (!vl)
-		return;
-
 	iov.iov_len = SVE_PT_SIZE(vq, SVE_PT_REGS_FPSIMD);
 	iov.iov_base = malloc(iov.iov_len);
 	if (!iov.iov_base) {