xtensa: update DMA-related Documentation/features entries

xtensa supports DMA API debug and contiguous DMA, mark it as such.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

Documentation/features/io/dma-api-debug/arch-support.txt

@@ -36,5 +36,5 @@
     |          um: | TODO |
     |   unicore32: | TODO |
     |         x86: |  ok  |
-    |      xtensa: | TODO |
+    |      xtensa: |  ok  |
     -----------------------

Documentation/features/io/dma-contiguous/arch-support.txt

@@ -36,5 +36,5 @@
     |          um: | TODO |
     |   unicore32: | TODO |
     |         x86: |  ok  |
-    |      xtensa: | TODO |
+    |      xtensa: |  ok  |
     -----------------------