Add a registry of open Serial Ports.

This will be used by components that need to pause an open serial
port to run some other functionality over the port. For example,
Arduino needs to pause the port to run the bootloader. This removes
the need for Serial ports to use o.e.remote.

Change-Id: Idb14598541ccf4e87c702cf2e5442335c64a6c65
2 files changed