CFAM read/write failure during ipl

[ojayanth]

Found issue in IPL path, if we do pdbg init and probe at start and CFAM reset during ipl window could trigger fsi read failure. Currently probe function skip the rescan function if it is already in known state.

[ojayanth]

istep 0 / istep poweron and attn code will need to handle fd's changing on cfam-reset/scan.
ecmd-pdbg need to make changes to initiate probe until after cfam-reset/scan ( Post poweron step in istep 0 sequence).
Long-running applications: SIGHUP to applications who have fd's cached? libpdbg would need a release interface or re-acquire state info. Pdbg library is going to provide interface to support this and application can consume.