net: airoha: Add airoha_ppe_get_num_stats_entries() and airoha_ppe_get_num_total_stat...

net: airoha: Add airoha_ppe_get_num_stats_entries() and airoha_ppe_get_num_total_stats_entries()

Introduce airoha_ppe_get_num_stats_entries and
airoha_ppe_get_num_total_stats_entries routines in order to make the
code more readable controlling if CONFIG_NET_AIROHA_FLOW_STATS is
enabled or disabled.
Modify airoha_ppe_foe_get_flow_stats_index routine signature relying on
airoha_ppe_get_num_total_stats_entries().

Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20251017-an7583-eth-support-v3-3-f28319666667@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>