mediatek: add script to trigger scrubbing of FIP-in-UBI

Read the 'fip' static volume in order to trigger scrubbing in case of
detecting flipped bits while reading.
We have to do this in Linux because we never read or touch the 'fip'
volume and the UBISPL implementation in ARM TrustedFirmware-A does NOT
handle scrubbing itself.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/base-files/lib/preinit/07_trigger_fip_scrubbing

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+trigger_fip_scrubbing() {
+	local vol voltype volname
+	for vol in /sys/class/ubi/ubi*_*; do
+		[ -e "$vol" ] || continue
+		voltype="$(cat "$vol"/type)"
+		volname="$(cat "$vol"/name)"
+		if [ "$voltype" = "static" ] && [ "$volname" = "fip" ]; then
+			cat "/dev/${vol##*/}" > /dev/null
+			break
+		fi
+	done
+}
+
+boot_hook_add preinit_main trigger_fip_scrubbing