net: ethernet: renesas: drop SoC names in Kconfig

Mentioning SoCs in Kconfig descriptions tends to get stale (e.g. RAVB is
missing RZV2M) or imprecise (e.g. SH_ETH is not available on all
R8A779x). Drop them instead of providing vague information. 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/20231022205316.3209-3-wsa+renesas@sang-engineering.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>