[ARM] 4057/1: ixp23xx: unconditionally enable hardware coherency

On ixp23xx, it was thought to be necessary to disable coherency to work
around certain silicon errata.  This turns out not to be the case --
none of the documented errata workarounds require disabling coherency,
and disabling coherency does not work around any existing errata.

Furthermore, all ixp23xx models do support coherency, so we should just
unconditionally enable coherency for all ixp23xx.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>