Move the rtpcs_link pointer array from rtpcs_ctrl (keyed by global
DSA port) into rtpcs_serdes (keyed by the per-SerDes link index).
This matches how the hardware is structured -- a SerDes hosts up to
RTPCS_MAX_LINKS_PER_SDS PCS links -- and aligns the in-driver
addressing with the cell the DTSes just gained on pcs-handle, so the
upcoming fwnode_pcs resolver becomes a direct sds->link[cell] lookup.
rtpcs_create() takes a new link_idx parameter and stores into
sds->link[link_idx] instead of ctrl->link[port]; the DSA glue switches
its phandle lookup to of_parse_phandle_with_args() and forwards the
cell. The port number stays on rtpcs_link for legacy callers that
still need it. Bounds and double-bind checks (-EINVAL, -EBUSY) guard
against malformed DT references that would otherwise OOB or silently
overwrite an existing link.
Drops RTPCS_PORT_CNT, whose only user was the relocated array, and
fixes a pre-existing of_node_put leak on the pcs-handle phandle in
the DSA glue as a side effect of the parse-with-args conversion.
Link: https://github.com/openwrt/openwrt/pull/23539
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>