selftests/rseq: riscv: Template memory ordering and percpu access mode

Introduce a rseq-riscv-bits.h template header which is internally included
to generate the static inline functions covering:

- relaxed and release memory ordering,
- per-cpu-id and per-mm-cid per-cpu data access.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221122203932.231377-18-mathieu.desnoyers@efficios.com