Documentation: arm: marvell: Extend Avanta list

Include another two SoCs from Avanta family.
Signed-off-by: NPali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20220121115804.28824-1-pali@kernel.orgSigned-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/arm/marvell.rst

@@ -266,10 +266,12 @@ Avanta family
 -------------
 
   Flavors:
+       - 88F6500
        - 88F6510
        - 88F6530P
        - 88F6550
        - 88F6560
+       - 88F6601
 
   Homepage:
 	https://web.archive.org/web/20181005145041/http://www.marvell.com/broadband/