Add read-only permissions on /data for petalinux

Adds the mode=0755 option to the /data fstab entry. This gives read permissions to the petalinux user to look at test results.

petalinux/meta-pbv3/recipes-core/base-files/base-files_%.bbappend

 dirs755 += "/data"
 
 do_install_append() {
-    echo "/dev/mmcblk0p2 /data auto defaults 0 0" >> ${D}${sysconfdir}/fstab
+    echo "/dev/mmcblk0p2 /data auto defaults,mode=0755 0 0" >> ${D}${sysconfdir}/fstab
     echo "overlay /etc overlay lowerdir=/etc,upperdir=/data/upper,workdir=/data/work 0 0" >> ${D}${sysconfdir}/fstab
 }