psplash: Add udev rule notify systemd of available fb

When using psplash in combination with systemd the splash screen is not
shown. The dependency to sys-devices-platform-gpu-graphics-fb0.device
will terminate psplash-start.service because systemd is not aware of the
framebuffer device node.
See https://lists.yoctoproject.org/g/yocto/topic/91286438#57156

Adding a udev rule to notify systemd

recipes-core/psplash/files/fb.rules

@@ -0,0 +1 @@
+SUBSYSTEM=="graphics", KERNEL=="fb0", TAG+="systemd"

recipes-core/psplash/psplash_%.bbappend

@@ -1,11 +1,15 @@
 FILESEXTRAPATHS:prepend := "${THISDIR}/files:"
 SPLASH_IMAGES:rpi = "file://psplash-raspberrypi-img.h;outsuffix=raspberrypi"
 
-SRC_URI:append:rpi = " file://framebuf.conf"
+SRC_URI:append:rpi = " \
+    file://framebuf.conf \
+    file://fb.rules \
+    "
 
 do_install:append:rpi() {
     if [ "${@bb.utils.filter('DISTRO_FEATURES', 'systemd', d)}" ]; then
         install -Dm 0644 ${WORKDIR}/framebuf.conf ${D}${systemd_system_unitdir}/psplash-start.service.d/framebuf.conf
+        install -Dm 0644 ${WORKDIR}/fb.rules ${D}${sysconfdir}/udev/rules.d/fb.rules
     fi
 }