GHES platform devices

[Bjorn Helgaas]

Hi Huang,

7ad6e9435596 ("ACPI, APEI, Manage GHES as platform devices") added
platform devices so the GHES driver could be built as a module and
automatically loaded when needed.

Later, 86cd47334b00 ("ACPI, APEI, GHES, Prevent GHES to be built as
module") removed the ability to build GHES as a module.

Should we revert 7ad6e9435596?  It's inconsistent to handle GHES, but
not other error sources, as a platform device.  And having it as a
platform device probably puts gunk in sysfs that we don't need.

Bjorn