ARM PJ4B: Add support for errata 4611

A CP15 clean operation can result in a dead lock state if it is hit by
an incoming snoop event. The fix to this issue is the following:
before any CP15 clean type operation in Cache Coherency mode, issue a
Data Memory Barrier (DMB) or a Data Synchronization Barrier (DSB)
instruction.

[gregory.clement@free-electrons.com:add errata description in changelog]
[gregory.clement@free-electrons.com:make this errata depend on Armada 370]
Signed-off-by: Lior Amsalem <alior@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>