riscv: Keep the riscv Kconfig selects sorted

riscv: Keep the riscv Kconfig selects sorted

Move three Kconfig selects: ARCH_STACKWALK, ARCH_SUPPORTS_ATOMIC_RMW
and ARCH_SUPPORTS_DEBUG_PAGEALLOC to the right place.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>