net: designware: add DMA offset awareness

Older DesignWare Ethernet MAC versions that this driver supports can
only work with 32-bit DMA source/destination addresses. Some platforms
have no physical RAM at the lowest 4GB address space. For these
platforms the driver must translate DMA addresses to/from physical
memory addresses.

Call translation routines so that properly configured platforms can use
the DesignWare Ethernet MAC. For platforms using device-tree this
usually means adding dma-ranges property to the bus the device node is
in.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>