kselftest/arm64: Specify SVE data when testing VL set in sve-ptrace

kselftest/arm64: Specify SVE data when testing VL set in sve-ptrace

Since f916dd32a943 ("arm64/fpsimd: ptrace: Mandate SVE payload for
streaming-mode state") we reject attempts to write to the streaming mode
regset even if there is no register data supplied, causing the tests for
setting vector lengths and setting SVE_VL_INHERIT in sve-ptrace to
spuriously fail. Set the flag to avoid the issue, we still support not
supplying register data.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250609-kselftest-arm64-ssve-fixups-v2-3-998fcfa6f240@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>