mvpp2: Fix warning over 32bit vs 64bit targets

When we have a driver that is used on both 32bit and 64bit targets and
we are talking about address space we cannot use u64 nor u32 and instead
need to use phys_addr_t.

Fixes: 377883f1 ("net: mvpp2x: fix phy connected to wrong mdio issue")
Cc: Stefan Chulski <stefanc@marvell.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>