net: ethernet: renesas: rcar_gen4_ptp: Hide register layout

net: ethernet: renesas: rcar_gen4_ptp: Hide register layout

With the support for multiple register layout removed all support
structures can be removed from the header file. Covert to a simpler
structure using defines for the register offsets.

There is no functional change, only switching from looking up offsets at
runtime to compile time.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250908154426.3062861-3-niklas.soderlund+renesas@ragnatech.se
Signed-off-by: Jakub Kicinski <kuba@kernel.org>