net: rswitch: Move definition of S4 gPTP offset

net: rswitch: Move definition of S4 gPTP offset

The files rcar_gen4_ptp.{c,h} implements an abstraction of the gPTP
support implemented together with different other IP blocks. The first
device added which supported this was RSWITCH on R-Car S4.

While doing so the RSWITCH R-Car S4 specific offset was added to the
generic Gen4 gPTP header file. Move it to the RSWITCH driver to make it
clear it only applies to this driver.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://patch.msgid.link/20251104222420.882731-2-niklas.soderlund+renesas@ragnatech.se
Signed-off-by: Jakub Kicinski <kuba@kernel.org>