docs: dev-tools: kmemleak: Update list of architectures

* Don't list powerpc twice (once as ppc)
* Drop tile, which has been removed from the source tree
* Mention arm64, nds32, arc, and xtensa
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20200303194215.23756-1-j.neuschaefer@gmx.netSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/kmemleak.rst

@@ -8,7 +8,8 @@ with the difference that the orphan objects are not freed but only
 reported via /sys/kernel/debug/kmemleak. A similar method is used by the
 Valgrind tool (``memcheck --leak-check``) to detect the memory leaks in
 user-space applications.
-Kmemleak is supported on x86, arm, powerpc, sparc, sh, microblaze, ppc, mips, s390 and tile.
+Kmemleak is supported on x86, arm, arm64, powerpc, sparc, sh, microblaze, mips,
+s390, nds32, arc and xtensa.
 
 Usage
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