gve: Add page size register to the register_page_list command.

gve: Add page size register to the register_page_list command.

This register is required on platforms with page sizes greater than 4k.
This is because the tx side of the driver vmaps the entire queue page
list of pages into a single flat address space, then uses the entire
space. Without communicating the guest page size to the backend, the
backend will only access the first 4k of each page in the queue page list.

Signed-off-by: Jordan Kimbrough <jrkim@google.com>
Signed-off-by: John Fraker <jfraker@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/r/20231128002648.320892-5-jfraker@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>