siflower: sf21: add support for Bananapi BPI-RV2

siflower: sf21: add support for Bananapi BPI-RV2

Specification:
 - Siflower SF21H8898
 - 512MB DDR3, 128MB SPI-NAND and 16MB SPI-NOR
 - 5x Gigabit ports (SF23P1240 QSGMII PHY and SF23P1211F RGMII PHY)
 - 1x 2.5G port (Airoha EN8811H PHY)
 - M.2 Key B slot with USB2.0, PCIEx1 and a NanoSIM card slot
 - MiniPCIe slot with USB2.0 and PCIEx1
 - 1x USB2.0 port through USB Hub
 - PCF8563-compatible RTC

The SoC can only boot from SPI0. Two SPI flash chipselects are connected
to GPIO5 (SPI0 CS) and GPIO36 through a 2x2 jumper. It boots from
SPI-NOR or SPI-NAND depending on how the jumpers are connected.

The firmware can be flashed using U-boot web recovery from Siflower
vendor U-boot.

Link: https://github.com/openwrt/openwrt/pull/17115
Signed-off-by: Chuanhong Guo <gch981213@gmail.com>