kselftest/arm64: Add coverage of TPIDR2_EL0 ptrace interface

kselftest/arm64: Add coverage of TPIDR2_EL0 ptrace interface

Extend the ptrace test support for NT_ARM_TLS to cover TPIDR2_EL0 - on
systems that support SME the NT_ARM_TLS regset can be up to 2 elements
long with the second element containing TPIDR2_EL0. On systems
supporting SME we verify that this value can be read and written while
on systems that do not support SME we verify correct truncation of reads
and writes.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220829154921.837871-5-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>