otpset: Fix reading OTP on BCM2712

[YORROY123]

On Pi 5 / CM5, vcgencmd otp_dump starts at row 00, skips rows 61-76 and 93-108, and uses three digit row numbers from 109 up. ReadOTP assumes the dump starts at row 08, is contiguous and that every row number has two digits (val[3:]), so on BCM2712:

• otpset -c and otpset -p crash:

  File "/usr/bin/otpset", line 72, in ReadOTP
    result[i] = int(val[3:], base=16)
  ValueError: invalid literal for int() with base 16: b':19a519a6'
  

• before the crash, otpset -c prints dump rows 28-35 as customer rows 0-7. On the CM5 below that shows the serial number as customer row 3 and the revision code as customer row 4, while the real customer OTP is all zero:

  $ sudo otpset -c
  ...
  3 0xea44e26e b'11101010010001001110001001101110
  4 0x00c04180 b'00000000110000000100000110000000
  ...
  $ sudo vcmailbox 0x00030021 40 40 0 8 0 0 0 0 0 0 0 0
  0x00000040 0x80000000 0x00030021 0x00000028 0x80000028 0x00000000 0x00000008 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000 0x00000000
  

This PR:

• parses the row number from each <row>:<value> line instead of using the line index
• reads the customer rows with the documented mailbox call (0x00030021) instead of assuming where they sit in the dump
• drops the BCM2711 row labels (Serial number, Revision code, ...) on BCM2712, where those rows hold other data

Tested on a CM5 (Compute Module 5 Rev 1.0, revision c04180, raspi-utils 20251120-1, Debian trixie):

Command	Before	After
otpset -c	wrong rows, then ValueError	8 rows, all zero, matches the mailbox read
otpset -p	ValueError	all 83 rows (0-60, 77-92, 109-114), exit 0
otpset -f -c / otpset -f -p		byte-identical to before
otpset -c / -p without sudo (user in video)		works
otpset -v -r 0 0x1 (dry run)		unchanged

I don't have a Pi 4 to hand, so the BCM2711 path is only covered by --fake; the mailbox read for -c is the one the OTP documentation gives for all models.

🤖 Generated with Claude Code

[YORROY123]

Also checked on a Pi 5, which has a newer package than the CM5 above (Raspberry Pi 5 Model B Rev 1.1, revision e04171, raspi-utils-otp 20260626-1, Debian trixie). Read-only commands only.

Command	/usr/bin/otpset (20260626-1)	this PR (cbe8ccc)
sudo otpset -c	rows 3/4/7 print 0x804afa61 / 0x00e04171 / 0xcec00454 (serial cec00454804afa61, revision e04171), then ValueError	8 rows, all zero, same as vcmailbox 0x00030021
sudo otpset -p	ValueError after row 60	83 rows (0-60, 77-92, 109-114), exit 0
otpset -c without sudo (user in video)		exit 0

So the crash is still there in the current package, and the same fix covers both BCM2712 boards I have.