drivers: eth: add support for NXP S32 GMAC

Add initial support for NXP S32 GMAC/EMAC:
- it's a copy-implementation with DMA data buffers and buffer
  descriptors in non-cached memory (buf len and ring size configurable)
- PHY interface selection only implemented for S32K3 devices as it is
  SoC-specific
- no PHY driver integration, it works as a fixed link with speed/duplex
  configured through devicetree
- supports multicast hash filtering, promiscuous mode, MAC loopback

Signed-off-by: Manuel Argüelles <manuel.arguelles@nxp.com>