board: gateworks: venice: dynamically update the update_firmware script

The update_firmware script is intended to update the boot firmware but
the details including the offset and hardware partition are dependent
on the boot device.

Specifically:
- IMX8MM/IMX8MP (BOOTROM v2) the offset is 32KiB for SD and eMMC user
  hardware partition and 0KiB for eMMC boot partitions.
- IMX8MM the offset is 33KiB for SD and eMMC regardless of hardware
  partition.

Dynamically set soc, dev, bootpart, and bootblk env vars at runtime
and use these in the update_firmware script. Remove the splblk env var
from config files as its no longer needed.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
diff --git a/board/gateworks/venice/venice.env b/board/gateworks/venice/venice.env
index 2054c02..a0d6c43 100644
--- a/board/gateworks/venice/venice.env
+++ b/board/gateworks/venice/venice.env
@@ -8,11 +8,11 @@
 dev=2
 preboot=gsc wd-disable
 console=ttymxc1,115200
-update_firmware=tftpboot $loadaddr $image &&
+update_firmware=tftpboot $loadaddr $dir/venice-$soc-flash.bin &&
 	setexpr blkcnt $filesize + 0x1ff &&
 	setexpr blkcnt $blkcnt / 0x200 &&
-	mmc dev $dev &&
-	mmc write $loadaddr $splblk $blkcnt
+	mmc dev $dev $bootpart &&
+	mmc write $loadaddr $bootblk $blkcnt
 loadfdt=if $fsload $fdt_addr_r $dir/$fdt_file1;
 	then echo loaded $fdt_file1;
 	elif $fsload $fdt_addr_r $dir/$fdt_file2;