kernel/arch/user_debugger: implement for risv64

Change-Id: I9cdf7a6a5b66cdd83133485f98067ce9a5fb819d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4058
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>

riscv64: Fill in more bulk architecture items around libroot/kernel

Change-Id: Ia2a86d8814d06950ea2d2d19d966c642d26f81d6
Reviewed-on: https://review.haiku-os.org/c/1302
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>