OpenSystemsDevelopment / usbboot

Add a Python utility script to converts RSA public keys
from PEM format to the binary format required by the bootloader
and vice-versa.

Check for a directory instead of a file.

rpi-eeprom-digest: Add an option to verify RSA signed files.

Wrap the OpenSSL commands to verify the RSA signature in a .sig
file for a given image. This could be used to verify a signed
boot image or EEPROM image before attempting to install it.

Merge https://github.com/timg236/cm4-scripts/pull/1 to remove the
LED activity flashing because this conflicts with EMMC_EN_N_1V8
on CM3.

I've reverted the change that removed the explict modprobe of
libcomposite becuase that broke the gadgetfs support for me on CM4.

Add option to look for CM with specific USB path.

Force device/peripheral mode instead of relying on the OTG pin
because this might not work on CM4S.

Replace duplicated bootcode4.bin with links to bootcode4.bin / recovery.bin

This also resolve a startup issue CM4-S

Sync this with the version in tools. TODO - change the scripts
to use the version in tools instead.

bootcode4: Improved DDR setup for old (or missing) EEPROM images

Ideally, the bootloader EEPROM should be updated before using
bootcode4 to run Linux so that full SDRAM init can be loaded.
This version fails over to a generic slow configuration if BRCM
DDR FW is not found.

Not all Linux systems have pkg-config installed by default, so include
it in the list of things to install.

Update Readme.md

Add missing products which do USB device boot.

Copy edit

Ensure consistency within repo and with style guide.

documentation: Secure boot quick start / walkthough

The secure-boot-example/boot.img has been replaced with the
mass-storage-gadget Linux OS image because it already supported
login, hdmi and ethernet.

Typo fixes from @dp111 (who obviously has too much time on his hands).

Revert binary to usbboot 4608d57c4d57dde19cc14988ee14702868d394bd

msd: Fix support for older EEPROM release in on 2711