rockchip: rk3576: Add SPI Flash boot support

rockchip: rk3576: Add SPI Flash boot support

The bootsource ids reported by BootROM of RK3576 for SPI NOR and USB
differs slightly compared to prior SoCs:

- Booting from sfc0 (ROCK 4D) report the normal bootsource id 0x3.
- Booting from sfc1 M1 (NanoPi M5) report a new bootsource id 0x23.
- Booting from sfc1 M0 has not been tested (no board using this config).
- Booting from USB report a new bootsource id 0x81.

Add a RK3576 specific read_brom_bootsource_id() function to help decode
the new bootsource id values and the required boot_devices mapping of
sfc0 and sfc1 to help support booting from SPI flash on RK3576.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>