IXP4xx: Always ioremap() Queue Manager MMIO region at boot.

It doesn't make much sense to map QMgr dynamically - we almost always need it
and the static mapping will be needed for little-endian data-coherent operation
(to make QMgr region value-coherent).

Signed-off-by: Krzysztof Hałasa <khc@pm.waw.pl>