arm: socfpga: misc: Add proper ethernet initialization

arm: socfpga: misc: Add proper ethernet initialization

Add function to initialize the EMAC blocks upon board startup.
The preprocessor guards against building on SoCFPGA-VT and against
SPL build are not needed as those are handled implicitly via both
SPL framework and the socfpga_cyclone5.h config file, which will
not define CONFIG_DESIGNWARE_ETH if building for SoCFPGA-VT.

We cannot handle two EMAC ethernet blocks yet, therefore the ifdefs.
Once there is hardware using both EMAC blocks, this ifdef will have
to go.

Signed-off-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <clsee@altera.com>
Cc: Dinh Nguyen <dinguyen@altera.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Tom Rini <trini@ti.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Pavel Machek <pavel@denx.de>