platform-drivers-x86 for v4.15-2

Fix two issues resulting from the dell-smbios refactoring and
introduction of the dell-smbios-wmi dispatcher. The first ensures a
proper error code is returned when kzalloc fails. The second avoids an
issue in older Dell BIOS implementations which would fail if the more
complex calls were made by limiting those platforms to the simple calls
such as those used by the existing dell-laptop and dell-wmi drivers,
preserving their functionality prior to the addition of the
dell-smbios-wmi dispatcher.

The following is an automated git shortlog grouped by driver:

dell-laptop:
 -  Fix error return code in dell_init()

dell-smbios-wmi:
 -  Disable userspace interface if missing hotfix
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