v1 passes the drive and partition number of the boot volume
instead of using the volume number. The volume number isn't
reliable because the same filesystem might get a different
volume number once the firmware is loaded, which will cause
the firmware to use the wrong root volume and fail to locate
the correct .rockbox directory.
Using drive and partition numbers avoids this issue because
drive numbering is fixed and determined by the target.
Change-Id: I7e68b892d9424a1f686197a6122e139b438e5f7e
Instead of verifying the CRC before every access of the boot data,
verify the CRC once at startup and set a flag to indicate the boot
data is valid.
Also add a framework to support multiple boot protocol versions.
Firmware declares the maximum supported protocol version using a
version byte in the boot data header. The bootloader chooses the
highest version supported by it and the firmware when deciding
what boot protocol to use.
Change-Id: I810194625dc0833f026d2a23b8d64ed467fa6aca
