pwr-mlxbf: support Bobcat graceful shutdown via gpio6

[Asmaa Mnebhi]

SRU Justification:

[Impact]

OCP3.0 project was discontinued and canceled so all stale code related to
that was removed.
The HID MLNXBF29 is used now for triggering a graceful shutdown for the Bobcat
board. On the bobcat board, the main board cpld issues the shutdown request to
the dpu cpld. the dpu cpld issues that request to ARM via GPIO6 and ARM should
trigger a graceful shutdown and set the ARM boot progress to 6.

[Fix]

The HID MLNXBF29 is used now for triggering a graceful shutdown for the Bobcat
board. On the bobcat board, the main board cpld issues the shutdown request to
the dpu cpld. the dpu cpld issues that request to ARM via GPIO6 and ARM should
trigger a graceful shutdown and set the ARM boot progress to 6.

[Test Case]

* Test shutdown on Bobcat via CPLD command.

[Regression Potential]

* no known regression as the OCP3.0 board was discontinued.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is awaiting verification that the linux-bluefield/5.15.0-1040.42 kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-jammy-linux-bluefield' to 'verification-done-jammy-linux-bluefield'. If the problem still exists, change the tag 'verification-needed-jammy-linux-bluefield' to 'verification-failed-jammy-linux-bluefield'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Khoa Vo (khoadvo)]

Verification does not have this type of board, we only validate changes did not break mlnx_gige on regular BF