mtd: remove pmcmsp-ramroot.c

The RAMROOT function was a successful but non-portable attempt to append
the root filesystem to the end of the kernel image.  The preferred and
portable solution is to use an initramfs instead.

The only user of this function was the msp71xx configuration
in the MIPS architecture; as the use of the RAMROOT has been removed
from that configuration, there are no more users, so this code
can be removed.

Signed-off-by: Shane McDonald <mcdonald.shane@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>