net: enetc: make enetc_set_rss_key() reusable

net: enetc: make enetc_set_rss_key() reusable

Since the offset of the RSS key registers of i.MX95 ENETC is different
from that of LS1028A, so add enetc_get_rss_key_base() to get the base
offset for the different chips, so that enetc_set_rss_key() can be
reused for this trivial thing.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20250506080735.3444381-8-wei.fang@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>