uml: add 6.12 testing kernel

uml: add 6.12 testing kernel

refresh config + patches.

This includes the following changes:
 - The selected x86_64 CPU is switched to generic instead of K8.

A backported patch is included from 6.13.

000-v6.13-asm-generic-io.h-rework-split-ioread64-iowrite64-hel.patch
|fixed the following build error:
|  CC      lib/iomap.o
|lib/iomap.c:156:5: error: no previous prototype for 'ioread64_lo_hi' [-Werror=missing-prototypes]
|  156 | u64 ioread64_lo_hi(const void __iomem *addr)
|      |     ^~~~~~~~~~~~~~
| [...]

Note: 102-pseudo-random-mac.patch will likely go away with the next stable.
UML is switching to a new networking infrastructure. The previous implementation
using tuntap, daemon, socket, ethertap, vde are being replaced by "vector"
transports tap, hybrid, raw, EoGRE, Eol2tpv3, fd, vde (vector!).

Please see, to checkout what will change:
<https://docs.kernel.org/virt/uml/user_mode_linux_howto_v2.html#setting-up-uml-networking>

Signed-off-by: Christian Lamparter <[email protected]>