rockchip: rk3588: Fix boot from SPI flash

The commit fd6e425b ("rockchip: rk3588-rock-5b: Enable boot from SPI
NOR flash") added a new BROM_BOOTSOURCE_SPINOR_RK3588 with value 6.

At the time the reason for this new bootsource id value 6 was unknown.

We now know that the BootRom on RK3588 use different bootsource id
values depending on the iomux used by the flash spi controller, and not
by the type of spi nor or spi nand flash used.

Add the following enum values and use them for RK3588 boot_devices.

- BROM_BOOTSOURCE_FSPI_M0 = 3
- BROM_BOOTSOURCE_FSPI_M1 = 4
- BROM_BOOTSOURCE_FSPI_M2 = 6

Fixes: fd6e425b ("rockchip: rk3588-rock-5b: Enable boot from SPI NOR flash")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Tested-by: Slawomir Stepien <sst@poczta.fm>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>