Add SCSI scan for ENV in EXT4 or FAT

When having environment stored in EXT4 or FAT
and using an AHCI or SCSI device / partition
the scan would not be performed early enough
and hence the device would not be recognized.
This change adds the scan when the interface
is "scsi" in a similar way to mmc_initialize.

Signed-off-by: Rogier Stam <rogier@unrailed.org>
Reviewed-by: Pali Rohár <pali@kernel.org>