OpenSystemsDevelopment / usbboot

* Add 2711 bootcode and FW binaries with the 4 suffix.
* Use the device descriptor to select the correct bootcode and
  hack it so that bootcode.bin translates to bootcode4.bin on a
  Pi4 allowing the files to remain in the same directory.
* Add the latest best for recovery.bin and pieeprom.bin for CM4
* Update the installer.

Move the second stage preparation until after the device descriptor
has been retrieved because BCM2711 needs a different bootcode.bin.

If the '-d' argument specified then check for bootcode.bin in the
specified directory and don't fail over to the embedded fmem files.

Remove the default 'msd' directory and the references to /usr/share
because the behaviour conflicts with the original change to use
the fmem files.