kernel: riscv64 patches

Change-Id: I8ebcbaa395cbccb50af08fd2f1b049b5cbb949c7
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3883
Reviewed-by: Fredrik Holmqvist <fredrik.holmqvist@gmail.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
Reviewed-by: X512 <danger_mail@list.ru>

kernel/riscv64: ATOMIC64 FUNCS are not syscalls

Change-Id: I8696939ec2fab6f3960a9a41f0b5c9fcd6949760
Reviewed-on: https://review.haiku-os.org/c/1379
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

kernel: Fill remaining riscv64 architecture headers