Not all versions of ESPRESSObin require SD card, but can
be booted from the internal emmc flash (mmc dev 1) instead.
Add a simple check in the bootscript to see which mmc device
is detected and boot from it using mmcdev variable.
Tested-by: Tomasz Maciej Nowak <tomek_n@o2.pl>
Signed-off-by: Vladimir Vid <vladimir.vid@sartura.hr>
(cherry picked from commit 008b41b9b0ddd4c5c877a769a85d27eb9c4e21a4)
886f524c6b