Linux 6.4

While we wait to see what Red Hat's new source code policy does to RHEL rebuilds like RockyLinux and Alma Linux downstream, Linux 6.4 came out this week. Aside from things like new hardware support, filesystem improvements (such as a small performance win for ext4) and more Rust code, and the removal of the old SLOB memory allocator, there's not a lot here on the Power ISA side this time around except for the removal of various older evaluation boards. Expect to see it in Fedora and more leading edge distributions shortly.