net: airoha: Move REG_GDM_FWD_CFG() initialization in airoha_dev_init()

Move REG_GDM_FWD_CFG() register initialization in airoha_dev_init
routine. Moreover, always send traffic PPE module in order to be
processed by hw accelerator.
This is a preliminary patch to enable netfilter flowtable hw offloading
on EN7581 SoC.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>