[POWERPC] memory cleanup

[POWERPC] memory cleanup

The following changes have been made:
  - htab is allocated by "order" using RMA size, soon it will be
    assigned memory.
  - keep track of RMA in terms of its allocated page struct and order
  - free htab and RMA memory in arch_domain_destroy()
  - get rid of PTEG FULL message, everyone thinks its a bug

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