uml: fix CONFIG_ALL_KMODS

uml: fix CONFIG_ALL_KMODS

building with CONFIG_ALL_KMODS unearthed all sorts of interesting
failures

ERROR: module 'crypto/chacha-x86_64.ko' is missing.
ERROR: module 'crypto/poly1305-x86_64.ko' is missing.
ERROR: module 'crypto/curve25519-x86_64.ko' is missing.
ERROR: module 'crypto/camellia-x86_64.ko' is missing.

These stem from the main UML Makefile.
|# UML only makes sense on linux
|ifeq ($(HOST_OS),Linux)
|  ifeq ($(HOST_ARCH),x86_64)
|
|ARCH:=x86_64
|BOARD:=uml

The modules in question define x86_64 optimized version and
the OpenWrt's buildsystem expects that these modules will be present.

SPI is not available due to the UML Architecture not setting HAS_IOMEM.
In the future, UML could get (virtualized) IOMEM and/or SPI could drop
the HAS_IOMEM dependency. A patch for the latter has been sent:
<https://lore.kernel.org/linux-spi/20250530234941.950431-1-chunkeey@gmail.com/T/#u>

mt76: Unfortunately, the firmware packages are picked up, but the
associated drivers can't be build because iowrite32+ioread32 are
not defined.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>