ravb: RAVB should select PAGE_POOL

ravb: RAVB should select PAGE_POOL

If CONFIG_PAGE_POOL is not enabled:

    aarch64-linux-gnu-ld: Unexpected GOT/PLT entries detected!
    aarch64-linux-gnu-ld: Unexpected run-time procedure linkages detected!
    aarch64-linux-gnu-ld: drivers/net/ethernet/renesas/ravb_main.o: in function `ravb_rx_ring_refill':
    ravb_main.c:(.text+0x8d8): undefined reference to `page_pool_alloc_pages'
    aarch64-linux-gnu-ld: ravb_main.c:(.text+0x944): undefined reference to `page_pool_alloc_frag'
    aarch64-linux-gnu-ld: drivers/net/ethernet/renesas/ravb_main.o: in function `ravb_ring_init':
    ravb_main.c:(.text+0x1d4c): undefined reference to `page_pool_create'

Fixes: 966726324b7b1400 ("net: ravb: Allocate RX buffers via page pool")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/fa61b464ae1aa7630e9024f091991937941d49f1.1718113630.git.geert+renesas@glider.be
Signed-off-by: Jakub Kicinski <kuba@kernel.org>