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

Documentation/admin-guide/kernel-parameters.txt

@@ -3513,6 +3513,9 @@
 
 	nr_uarts=	[SERIAL] maximum number of UARTs to be registered.
 
+	numa=off 	[KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
+			set up a single NUMA node spanning all memory.
+
 	numa_balancing=	[KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
 			NUMA balancing.
 			Allowed values are enable and disable