In the current codes, the octeontx2 uses its own method to allocate
the pool buffers, but there are some issues in this implementation.
1. We have to run the otx2_get_page() for each allocation cycle and
   this is pretty error prone. As I can see there is no invocation
   of the otx2_get_page() in otx2_pool_refill_task(), this will leave
   the allocated pages have the wrong refcount and may be freed wrongly.
2. It wastes memory. For example, if we only receive one packet in a
   NAPI RX cycle, and then allocate a 2K buffer with otx2_alloc_rbuf()
   to refill the pool buffers and leave the remain area of the allocated
   page wasted. On a kernel with 64K page, 62K area is wasted.

IMHO it is really unnecessary to implement our own method for the
buffers allocate, we can reuse the napi_alloc_frag() to simplify
our code.
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>