board: ti: am62x: am62x.env: Add explicit boot_targets

Add explicit boot_targets to indicate the specific boot sequence to
follow.

NOTE: The non-standard ti_mmc emulates what is done for distro_boot.
With bootstd, this will eventually need to be replaced by equivalent
class.

Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
1 file changed