pwr-mlxbf: support graceful reboot instead of soft reset

[Asmaa Mnebhi]

SRU Justification:

[Impact]

There is a new feature request to replace the soft reset with a graceful reboot.
We will use acpi events triggered by the irq in the pwr-mlxbf file to trigger the graceful reboot.

[Fix]

* Change the handling of GPIO7 (BF2) and GPIO6 (BF3). This gpio will trigger a graceful reboot instead of
  a forced reboot (soft reset). This is an acpi event.

[Test Case]

* trigger the gpio toggling from the BMC: ipmitool raw 0x32 0xA1 0x02
  This should trigger a graceful reboot of the DPU.

[Regression Potential]

* make sure it works on BF2 and BF3

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

This bug is awaiting verification that the linux-bluefield/5.15.0-1031.33 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!