Add a -c file option to the vkernel to specify CD images. The first -c or -r

Add a -c file option to the vkernel to specify CD images.  The first -c or -r
option will be the boot device.

Add a new virtual CDRom device, vcd.  Basically its works the same as VKD
but we open the device in read-only mode and use a block size of 2048 instead
of 512.

Install the console as a real device and change the console major to be
the same as the syscons major so a default init is able to start up a getty.