Add support for the 16-way L310 L2 cache controller

[Will Deacon]

Hi Jason,

The patch entitled `Add support for the 16-way L310 L2 cache controller'
which you submitted to RMK's patch system appears to perform a 16-way
invalidation even when the ways might not be present. This results in
writes to the reserved bits [15:8] of the invalidate-by-way ctrl register.

You can check the associativity by reading bit 16 of the auxiliary ctrl
register.

Will