[XEN][POWERPC] memory clean up (phase 3)

[XEN][POWERPC] memory clean up (phase 3)

    The following changes are included:
     Open Firmware:
      - use all args for of_claim()
      - handle broken claim methods as best we can
      - describe where the Dom0 image is comming from
      - stop copying the Dom0 image

     Heaps:
      - make sure we do not overwrite the oftree
      - release as much memory as possible to xenheap
      - release Dom0 image after we are done with it
      - Lots of checks and simplifications

Signed-off-by: Jimi Xenidis <jimix@watson.ibm.com>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>