drivers: eth: sam-e70: revision B has more queues

The first revision of the SAM E70 soc had three queues. The current
revision B has six queues. If we don't initialize all queues, the DMA
engine gets stuck when trying to read a descriptor from NULL. To enable
the initialization of the additional queues, the correct soc has to be
selected in the config options, f.ex. CONFIG_SOC_PART_NUMBER_SAME70Q21B
instead of CONFIG_SOC_PART_NUMBER_SAME70Q21.

Also rename GMAC_QUEUE_NO to GMAC_QUEUE_NUM as requested during review.

Signed-off-by: Daniel Glöckner <dg@emlix.com>