main/linux-vanilla: Enable CONFIG_UEVENT_HELPER for s390x.

The config option is required for busybox's mdev to work, or we'll get ".../lib/rc/sh/openrc-run.sh: line 21: can't create /proc/sys/kernel/hotplug: nonexistent directory" on boot.

main/linux-vanilla/APKBUILD

@@ -229,7 +229,7 @@ f91a1f3fb9d17697a7edab09587ec9e933950460362141409b64c0537e8998f50c1c998388ab0d29
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 96651aca476c905c04d616565a2dd08066167c1d4887e2ddc86c4b7cdda44257ef633a9bcf745a91f00f88023dde8f1804c56b258e7e99232bb8bfa25d0ba4db  config-vanilla.ppc
 a86d89a0060e91d14d6943683d3846ef047f9f483e7c58d061aac745bade0324c5c24f60ad3046cd45e87e7e80a31d1f6d6c3477464d2d3066b9fb50a6d000d4  config-vanilla.ppc64le
-f370c3431d8e6256433d30cf6614d341a36c3b74cd597e49ad1db6b501529831c9bf02c88887bdbb35ea7d909eda74d42208d39ce97ae8688edb372db12b48ac  config-vanilla.s390x
+e2bfae0e0086c3961abb9f08e185095a54ebd97ac1fa326f3162e10c6945b12632033ba371f9e326cda9b31ad7f7017c1cd0accdf1e78fcc9c44dc66e3e3caaa  config-vanilla.s390x
 739ecce3d1a17a56efbedb2d3eccf19403b6e0455327b659ceedc9df6291f15c5666e6d130e76e7a93cb7f1a410f94865a0d8a4de1c0008a1a45575d1e9d2cc0  config-virt.aarch64
 4984ac56593d2a2b6f4bc3aee15c5a528d2192730d18257e5ac1849551ff71f2008611859e5d751e50b6841581e3f72634551b526d754ad3745f36306a9c7dab  config-virt.x86
 e759bb530c39f091f1dd5b82e8c0a851016f68e2ba0986ae12015bf9581de2ef29dd6e1625b72eabab7ac718c50b3d32e24bf29628de3a94eec4d152e00ddd4a  config-virt.x86_64

main/linux-vanilla/config-vanilla.s390x

@@ -1374,7 +1374,8 @@ CONFIG_HAVE_EBPF_JIT=y
 #
 # Generic Driver Options
 #
-# CONFIG_UEVENT_HELPER is not set
+CONFIG_UEVENT_HELPER=y
+CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
 CONFIG_DEVTMPFS=y
 # CONFIG_DEVTMPFS_MOUNT is not set
 CONFIG_STANDALONE=y