[XEN][POWERPC] Early boot memory avoidance improvemnts

[XEN][POWERPC] Early boot memory avoidance improvemnts
This patch add a simple memory allocator that can be used to:
  - repect our loaded image
  - repect firmware suggestions on "availble" memory
  - avoid memory we know to have issues with various different FW
Also cleans up a lot of the previous logic and no longer updates the
multipboot memory map since that is no longer used anyway.
Signed-off-by: Jimi Xenidis <jimix@watson.ibm.com>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
--HG--
extra : transplant_source : %CE%8C%1E%26%B2%AE%BDd%C8%A2%F0.%20%EDF%D5%87%F4%28p