net: xilinx_axi_emac: Use readl and writel for io ops

This patch uses readl and writel instead of in_be32 and
out_be32 for io ops as these internally uses readl,
writel for microblaze and for Zynq, ZynqMP there is
no need of endianness conversion and readl, writel
should work straightaway. This patch starts supporting
the driver for Zynq and ZynqMP platforms.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>