soc_id content according to specification

[Andrew Lunn]

> 2014 March:
> 56a705a48eae ("ARM: mvebu: Add a SOC bus device entry")
> => 16-bit hexadecimal PCI-E device ID?

Just for clarification here. The PCE-E ID is the same as the SoC
model. So for example, the Kirkwood MV88f6281 has a PCI product id of
6281. The Armada XP mv88f78230 has a PCI product id of 8230.

      Andrew