rpi-default-versions: Switch default kernel to 6.12

Signed-off-by: Markus Volk <f_l_k@t-online.de>

conf/machine/include/rpi-default-versions.inc

@@ -1,4 +1,4 @@
 # RaspberryPi BSP default versions
 
-PREFERRED_VERSION_linux-raspberrypi ??= "6.6.%"
+PREFERRED_VERSION_linux-raspberrypi ??= "6.12.%"
 PREFERRED_VERSION_linux-raspberrypi-v7 ??= "${PREFERRED_VERSION_linux-raspberrypi}"