The intention of the code block was to set MAC address for SPI
Ethernet modules, however !CONFIG_EXAMPLE_USE_INTERNAL_ETHERNET also
affected the case of CONFIG_EXAMPLE_USE_OPENETH.
This commit corrects the code to match the original intention.
Related to https://github.com/espressif/qemu/issues/107
Fixed memory leak in emac_esp_new_dma function.
Polished ESP EMAC cache management.
Added emac_periph definitions based on SoC features and improved(generalized) ESP EMAC GPIO
initialization.
Added ESP EMAC GPIO reservation.
Added check for frame error condition indicated by EMAC DMA and created a target test.
