selftests: futex: Add tests for robust release operations

Add tests for __vdso_futex_robust_listXX_try_unlock() and for the futex()
op FUTEX_ROBUST_UNLOCK.

Test the contended and uncontended cases for the vDSO functions and all
ops combinations for FUTEX_ROBUST_UNLOCK.

[ tglx: Replace the VDSO function lookup ]

Signed-off-by: André Almeida <andrealmeid@igalia.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260329-tonyk-vdso_test-v2-2-b7db810e44a1@igalia.com