rqspinlock: Add macros for rqspinlock usage

Introduce helper macros that wrap around the rqspinlock slow path and
provide an interface analogous to the raw_spin_lock API. Note that
in case of error conditions, preemption and IRQ disabling is
automatically unrolled before returning the error back to the caller.

Ensure that in absence of CONFIG_QUEUED_SPINLOCKS support, we fallback
to the test-and-set implementation.

Add some comments describing the subtle memory ordering logic during
unlock, and why it's safe.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20250316040541.108729-17-memxor@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>