ACPICA: Remove obsolete debug levels (WARN and ERROR)

Removed ACPI_DB_WARN and ACPI_DB_ERROR. These debug levels were
made obsolete by the ACPI_WARNING and ACPI_ERROR/ACPI_EXCEPTION
interfaces.  Also added ACPI_DB_EVENTS to correspond with the
existing ACPI_LV_EVENTS.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>