net: ftgmac100: Add optional reset control for RMII mode on Aspeed SoCs

net: ftgmac100: Add optional reset control for RMII mode on Aspeed SoCs

On Aspeed SoCs, the internal MAC reset is insufficient to fully reset the
RMII interface; only the SoC-level reset line can properly reset the RMII
logic. This patch adds support for an optional "resets" property in the
device tree, allowing the driver to assert and deassert the SoC reset line
when operating in RMII mode. This ensures the MAC and RMII interface are
correctly reset and initialized.

Signed-off-by: Jacky Chou <jacky_chou@aspeedtech.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250709070809.2560688-5-jacky_chou@aspeedtech.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>