rockchip: puma-rk3399: fix boot_targets swap depending on U-Boot proper load medium

rockchip: puma-rk3399: fix boot_targets swap depending on U-Boot proper load medium

distroboot should try first on the same MMC medium as the one the SPL
loaded U-Boot proper from. This was the case when the introducing commit
was merged because the default order was eMMC first and then SD card.
The check was therefore made only on whether we booted from SD card,
because otherwise the order was the expected one.
However, in commit b212ad24a604 ("rockchip: Fix MMC boot order"), the
order was swapped. Meaning our simple check is now useless.

Let's fix that by accounting for all scenarii: default boot_targets has
mmc0 first but booting from SD Card, mmc1 first but booting from eMMC.

Fixes: b212ad24a604 ("rockchip: Fix MMC boot order")
Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>