arm64/signal: Use system_supports_tpidr2() to check TPIDR2

Since commit a9d69158("arm64/sme: Implement support
for TPIDR2"), We introduced system_supports_tpidr2() for
TPIDR2 handling. Let's use the specific check instead.

No functional changes.

Signed-off-by: Dongxu Sun <sundongxu3@huawei.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230317124915.1263-2-sundongxu3@huawei.com


Signed-off-by: Will Deacon <will@kernel.org>