acpi/ghes: Cleanup the code which gets ghes ged state

acpi/ghes: Cleanup the code which gets ghes ged state

Move the check logic into a common function and simplify the
code which checks if GHES is enabled and was properly setup.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-ID: <2bbb1d3eb88b0a668114adef2f1c2a94deebba0e.1758610789.git.mchehab+huawei@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>