net: stmmac: add platform init/exit for Altera's ARM socfpga

This patch adds platform init/exit functions and modifications to support
suspend/resume for the Altera Cyclone 5 SOC Ethernet controller. The platform
exit function puts the controller into reset using the socfpga reset
controller driver. The platform init function sets up the Synopsys mac by
first making sure the Ethernet controller is held in reset, programming the
phy mode through external support logic, then deasserts reset through
the socfpga reset manager driver.

Signed-off-by: Vince Bridgers <vbridgers2013@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>