ARM: mvebu: Use system controller to get the soc id when possible

ARM: mvebu: Use system controller to get the soc id when possible

On Armada 38x it is possible to get the SoC Id and the revision
without using the PCI register. Accessing the PCI registers implies
enabling its clock and, because of the initialization issue, not
keeping them enable. So if possible it is better to avoid it.

Armada 370 and Armada XP provides the SoC ID values from the system
controller but not the revision.

Armada 375 provides both but the SoC ID value looks buggy (0x6660
instead of 0x6720).

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Link: https://lkml.kernel.org/r/1403538128-27859-1-git-send-email-gregory.clement@free-electrons.com
Signed-off-by: Jason Cooper <jason@lakedaemon.net>