net: ethernet: renesas: group entries in Makefile

A new Renesas driver shall be added soon. Prepare the Makefile by
grouping the specific objects to the Kconfig symbol for better
readability. Improve the file description a tad while here.
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20231022205316.3209-2-wsa+renesas@sang-engineering.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/renesas/Makefile

 # SPDX-License-Identifier: GPL-2.0
 #
-# Makefile for the Renesas device drivers.
+# Makefile for the Renesas network device drivers
 #
 
 obj-$(CONFIG_SH_ETH) += sh_eth.o
 
 ravb-objs := ravb_main.o ravb_ptp.o
-
 obj-$(CONFIG_RAVB) += ravb.o
 
 rswitch_drv-objs := rswitch.o rcar_gen4_ptp.o
-
 obj-$(CONFIG_RENESAS_ETHER_SWITCH) += rswitch_drv.o