docs: remove all references to AVR32 architecture

The AVR32 architecture support has been removed from the Linux kernel,
hence remove all references to it from Documentation.

Signed-off-by: Hans-Christian Noren Egtvedt <egtvedt@samfundet.no>
Signed-off-by: Håvard Skinnemoen <hskinnemoen@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>

Documentation/features/vm/THP/arch-support.txt

@@ -10,7 +10,6 @@
     |         arc: |  ok  |
     |         arm: |  ok  |
     |       arm64: |  ok  |
-    |       avr32: |  ..  |
     |    blackfin: |  ..  |
     |         c6x: |  ..  |
     |        cris: |  ..  |