dt-bindings: net: starfive,jh7110-dwmac: Add JH7100 SoC compatible

The Synopsys DesignWare MAC found on StarFive JH7100 SoC is mostly
similar to the newer JH7110, but it requires only two interrupts and a
single reset line, which is 'ahb' instead of the commonly used
'stmmaceth'.

Since the common binding 'snps,dwmac' allows selecting 'ahb' only in
conjunction with 'stmmaceth', extend the logic to also permit exclusive
usage of the 'ahb' reset name.  This ensures the following use cases are
supported:

  JH7110: reset-names = "stmmaceth", "ahb";
  JH7100: reset-names = "ahb";
  other:  reset-names = "stmmaceth";

Also note the need to use a different dwmac fallback, as v5.20 applies
to JH7110 only, while JH7100 relies on v3.7x.

Additionally, drop the reset description items from top-level binding as
they are already provided by the included snps,dwmac schema.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>