siflower: sf21: new subtarget for sf21a6826/sf21h8898
Siflower SF21A6826/SF21H8898 are a family of RISC-V SoCs with:
* Quad-core T-Head C908 (1.125G for SF21A6826, 1.25G for SF21H8898)
* DDR3/DDR4 memory controller
* 1 QSGMII 4x1G
* 1 SGMII/2500Base-X 2.5G
* 1 additional RGMII on SF21H8898
* Network offloading engine for L2 switching and L3 NAT
* 2 PCIE Gen2 lanes, operating in either one PCIE Gen2x2 or two
PCIE Gen2x1 mode
* 1 USB2.0
Link: https://github.com/openwrt/openwrt/pull/17115
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>