soc/fsl/qbman: use ioremap_cache() instead of ioremap_prot(0)

ioremap_prot() with flag set to 0 relies on a hack in
__ioremap_caller() which adds PAGE_KERNEL flags when the
handed flags don't look like a valid set of flags
(ie don't include _PAGE_PRESENT)

The intention being to map cached memory, use ioremap_cache() instead.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>