net: lan96x: Use page_pool API

Use the page_pool API for allocation, freeing and DMA handling instead
of dev_alloc_pages, __free_pages and dma_map_page.

Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>