docs: kernel-parameters: mark numa=off is supported by a bundle of architectures

risc-v and arm64 support numa=off by common arch_numa_init()
in drivers/base/arch_numa.c. x86, ppc, mips, sparc support it
by arch-level early_param.
numa=off is widely used in linux distributions. it is better
to document it.

Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Link: https://lore.kernel.org/r/20210524051715.13604-1-song.bao.hua@hisilicon.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>