branch-merge: support device rotation

On some devices the LCD panel is mounted in the casing in such a way
that the up/top side of the panel does not match with the top side of
the device.

Examples of this are:
-Tablets where the LCD panel is mounted upside-down (various models)
-Clamshell design devices use portrait tablet screens in a landscape fashion /
 a landscape case, e.g. the GPD pocket, GPD win, Asus T100HA and the VIOS LTH17
 (so the didplay is mounted rotated 90 degrees clock-wise or counter-clock-wise).

Starting with kernel 4.16 there is code in the kernel to:
-Detect affected devices
-Automatically rotate the fbconsole to compensate
-Let userspace know about this with a new "panel orientation" property on the drm connector of the panel

The patch series I'm attaching to this bug adds support for this to
plymouth, so that the boot-splash and diskcrypt-ask-password are shown
with the correct orientation / the right way up on these devices.