kselftest/arm64/mte: Register mte signal handler with SA_EXPOSE_TAGBITS

kselftest/arm64/mte: Register mte signal handler with SA_EXPOSE_TAGBITS

To test address tag[63:60] and memory tag[59:56] is preserved
when memory tag fault happen, Let mte_register_signal() to register
signal handler with SA_EXPOSE_TAGBITS.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250618084513.1761345-6-yeoreum.yun@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>