docs: arm64: Move arm64 documentation under Documentation/arch/

Architecture-specific documentation is being moved into Documentation/arch/
as a way of cleaning up the top-level documentation directory and making
the docs hierarchy more closely match the source hierarchy.  Move
Documentation/arm64 into arch/ (along with the Chinese equvalent
translations) and fix up documentation references.

Cc: Will Deacon <will@kernel.org>
Cc: Alex Shi <alexs@kernel.org>
Cc: Hu Haowen <src.res@email.cn>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Yantengsi <siyanteng@loongson.cn>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/sysctl/kernel.rst

@@ -949,7 +949,7 @@ user space can read performance monitor counter registers directly.
 
 The default value is 0 (access disabled).
 
-See Documentation/arm64/perf.rst for more information.
+See Documentation/arch/arm64/perf.rst for more information.
 
 
 pid_max