memory-provider: disable building dmabuf mp on !CONFIG_PAGE_POOL

When CONFIG_TRACEPOINTS=y but CONFIG_PAGE_POOL=n, we end up with this
build failure that is reported by the 0-day bot:

ld: vmlinux.o: in function `mp_dmabuf_devmem_alloc_netmems':
>> (.text+0xc37286): undefined reference to `__tracepoint_page_pool_state_hold'
>> ld: (.text+0xc3729a): undefined reference to `__SCT__tp_func_page_pool_state_hold'
>> ld: vmlinux.o:(__jump_table+0x10c48): undefined reference to `__tracepoint_page_pool_state_hold'
>> ld: vmlinux.o:(.static_call_sites+0xb824): undefined reference to `__SCK__tp_func_page_pool_state_hold'

The root cause is that in this configuration, traces are enabled but the
page_pool specific trace_page_pool_state_hold is not registered.

There is no reason to build the dmabuf memory provider when
CONFIG_PAGE_POOL is not present, as it's really a provider to the
page_pool.

In fact the whole NET_DEVMEM is RX path-only at the moment, so we can
make the entire config dependent on the PAGE_POOL.

Note that this may need to be revisited after/while devmem TX is
added,  as devmem TX likely does not need CONFIG_PAGE_POOL. For now this
build fix is sufficient.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409131239.ysHQh4Tv-lkp@intel.com/
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Simon Horman <horms@kernel.org> # build-tested
Link: https://patch.msgid.link/20240913060746.2574191-1-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/Kconfig

@@ -70,6 +70,7 @@ config NET_DEVMEM
 	def_bool y
 	depends on DMA_SHARED_BUFFER
 	depends on GENERIC_ALLOCATOR
+	depends on PAGE_POOL
 
 menu "Networking options"