* arm_loader: Add machine ID derived from OTP values
Machine ID is generated and exposed in device tree as rpi-machine-id
* arm_ldconfig: Avoid double os_prefix on initramfs
When using auto_initramfs we were picking up prefix from the kernel,
but also adding os_prefix later:
fname = prefixed_path(initramfs_file, os_prefix, temp_path, sizeof(temp_path));
See: https://forums.raspberrypi.com/viewtopic.php?t=394238
* recovery: Use OTP rpiboot GPIO if non-zero
If an rpiboot GPIO has already been written to OTP then default to
that value if C(program_rpiboot_gpio) is not specified on config.txt.
