RAM block device is an implementation of the block-session interface
running as a client of a RAM session. It either populates the RAM dataspace
by using a ROM dataspace, similiar to loop devices. For example to use
an ISO file the component has to be configured as follows:

! <config file="image.iso" block_size="2048"/>

To use a empty RAM dataspace that is 256MiB large and has a block size
of 4KiB the configuration looks like this:

! <config size="256M" block_size="4096"/>

Either 'size' or 'file' has to specified. If both are declared the 'file'
attribute is soley evaluated.