net: macb: Add big endian CPU support

This patch converts all __raw_readl and __raw_writel function calls
to their corresponding readl_relaxed and writel_relaxed variants.

It also tells the driver to set ahb_endian_swp_mgmt_en bit in dma_cfg
when the CPU is configured in big endian mode.

Signed-off-by: Arun Chandran <achandran@mvista.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>