board/orangepi/orangepi-zero: using PARTUUID to identify root filesystem

The mmc block device number can vary, so passing a mmc block device to
specify the location of the rootfs is not a reliable
approach. Instead, use the root=PARTUUID=<uuid> mechanism, where the
uuid is found by U-Boot.

Signed-off-by: Sergey Kuzminov <kuzminov.sergey81@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/orangepi/orangepi-zero/boot.cmd

@@ -1,6 +1,7 @@
 setenv fdt_high ffffffff
 
-setenv bootargs console=ttyS0,115200 earlyprintk root=/dev/mmcblk0p2 rootwait
+part uuid mmc 0:2 uuid
+setenv bootargs console=ttyS0,115200 root=PARTUUID=${uuid} rootwait
 
 fatload mmc 0 $kernel_addr_r zImage
 fatload mmc 0 $fdt_addr_r sun8i-h2-plus-orangepi-zero.dtb