Update for "orphan" embedded controller _REG method support.

This refers to _REG methods under the EC device that have no
corresponding operation region. This is allowed by the ACPI
specification. This update removes a dependency on having an
ECDT table, and will execute an orphan _REG method as long as
the handler for the EC is installed at the EC device node
(not the namespace root).
Rui Zhang (original update), Bob Moore (update/integrate).
Debugger: Enhance "handlers" command to display non-root handlers.

This change enhances the handlers command to display handlers
associated with individual devices throughout the namespace, in
addition to the currently supported display of handlers associated
with the root namespace node.
AcpiExec: Add support for multiple embedded controllers.

This change installs operation region handlers for multiple embedded
controllers that the DSDT may support. All EC handlers are now
installed at the individual EC device nodes, instead of a single
EC handler installed at the root. This reflects the typical installation
of EC operation region handler(s) by host operating systems.