ACPI: APEI: Don't warn if ACPI is disabled

If ACPI is not enabled but support for ACPI and APEI is enabled in the
kernel, then the following warning is seen on boot ...

 WARNING KERN EINJ: ACPI disabled.

For ARM64 platforms, the 'acpi_disabled' variable is true by default
and hence, the above is often seen on ARM64. Given that it can be
normal for ACPI to be disabled, make this an informational print rather
that a warning.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>