Add GPIO interrupt enable for Z9100/S6100 and transceiver-plug-inout-…

[padmanarayana]

…event for Z9100

- What I did

1. Add GPIO interrupt support for S6100 & Z9100 platforms.
2. get_transceiver_change_event for Z9100

- How I did it
Z9100/S6100 use GPIO SUS6 for edge triggered interrupts from the CPLDs for optics events (include module plug-in/out). Since they can't generate an IRQ, an SCI is enabled.

1. Add dell_ich module : this essentially exposes all necessary GPIO settings along with the relevant ACPI & PMC registers that are required to route the GPIO interrupt as an SCI. Also, if it’s a Z9100/S6100, do necessary initializations to route the GPIO event triggers as an SCI for SUS6. The SCI interrupt will essentially notify clients based on a sysfs attribute.
2. Dell_z9100_cpld.c and dell_s6100_iom_cpld.c : add the sysfs attributes to manipulate the interrupt, interrupt status and mask registers.
3. Update the z9100_platform.sh and s6100_platform.sh to unmask the module presence interrupts.
4. Update sfputil.py on Z9100 to wait on the SCI interrupt and emit the port dict for OIR events.

Note : get_transceiver_change_event support for S6100 is pending testing.

- How to verify it

Checked that port_dict emits the correct plug-in/plug-out event for the relevant port.

- Description for the changelog

Add GPIO interrupt enable for Z9100/S6100

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