gve: convert to use netmem for DQO RDA mode

gve: convert to use netmem for DQO RDA mode

To add netmem support to the gve driver, add a union
to the struct gve_rx_slot_page_info. netmem_ref is used for
DQO queue format's raw DMA addressing(RDA) mode. The struct
page is retained for other usecases.

Then, switch to using relevant netmem helper functions for
page pool and skb frag management.

Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Harshitha Ramamurthy <hramamurthy@google.com>
Link: https://patch.msgid.link/20250307003905.601175-1-hramamurthy@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>