download/u-boot: Support running extra commands from board dirs

Although it's unlikely, boards might want to run extra commands after
the board-specific U-Boot directories are prepared. Copy the existing
mechanism for that from the coreboot download script to the U-Boot one.

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>

resources/scripts/download/u-boot

@@ -183,6 +183,21 @@ downloadfor() {
 			return 1
 		fi
 	done
+
+	# extra.sh could be used to patch submodules, if you wanted to
+	# It's impossible to predict what submodules will be available, and
+	# it's rare that you'd want to patch them, so this is handled by
+	# extra.sh on a per-board basis
+	# In fact, extra.sh can be used for anything you want.
+	if [ -f "resources/u-boot/${board}/extra.sh" ]; then
+		"resources/u-boot/${board}/extra.sh" || touch build_error
+		if [ -f build_error ]; then
+			return 1
+		fi
+		return 0
+	else
+		return 0
+	fi
 }
 
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