Documentation: arm: update Marvell product listing

I'm still getting confused regarding which core specifically
is used in which SoC, so I've added some more detail to the
Marvell README file. I got most of this from random sources
on the internet, so it's possible that some of the information
is wrong, but most of it should be pretty obvious.

There are a few remaining points I could not find out:

* The CPU core in Orion 88F6183
* The difference (if any) between PJ4B-MP and PJ4C
* The naming of Feroceon/Jolteon/Flareon/Sheeva/Mohawk/PJ1/PJ4
  is still confusing, as they tend to overlap.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[Thomas:
 - move Armada SP out from the EBU family into its own "Storage"
   family. This chip is indeed not part of the EBU family.
 - fixed the URL for the Armada SP information, since the link of the
   original patch no longer existed
 - explicitly indicate that there is no support in upstream for the
   Armada SP
 - indent the "Core: " description for the Armada XP to be clearly
   under the Armada XP category, so that it is clear it applies to
   Armada XP only, and not other cores of the EBU family.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>