generic-uboot-tftp-ramdisk-preempt-rt-template.jinja2: Add missing template

As reported in issue #1307
We have error that this template is missing and many preempt-rt tests are
not being execute.

Signed-off-by: Denys Fedoryshchenko <denys.f@collabora.com>

Author: nuclearcat

config/lava/preempt-rt/generic-uboot-tftp-ramdisk-preempt-rt-template.jinja2

@@ -0,0 +1,7 @@
+{% extends 'boot/generic-uboot-tftp-ramdisk-boot-template.jinja2' %}
+{% block actions %}
+{{ super () }}
+
+{% include 'preempt-rt/preempt-rt.jinja2' %}
+
+{% endblock %}