xm-test: ia64 min memory & arbitrarily large ramdisk

xm-test: ia64 min memory & arbitrarily large ramdisk

1) Sets a minimum of 128MB RAM for an ia64 domU; this limit was set
after experimentation, which seems to indicate it's a reasonable lower
limit (the 32MB limit previously in place did not allow an ia64 domU
to start).  If there's any problem with this, I don't mind splitting
the patch and sending it to the ia64 list, but it was small, so I hope
it's okay to include it.

2) xm-test uses ramdisks built with uClibc, which doesn't compile on
ia64.  I was able to create a ramdisk by hand, but as it was too
large, the resultant domU crashed after boot.  This patch enables the
use of an arbitrarily large ramdisk, so long as it's uncompressed.  As
xm-test builds only uncompressed ramdisks, I figured this was
reasonable for that specific application.  Suggestions on how to
detect and handle a compressed ramdisk would be welcome.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>