kselftest/arm64: add FEAT_LSE128 to hwcap test

Add test of a 128-bit atomic instruction for FEAT_LSE128.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20231003124544.858804-3-joey.gouly@arm.com


[catalin.marinas@arm.com: reordered lse128_sigill() alphabetically]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>