CA-31930: fix balloon handling for domain 0
CA-31930: fix balloon handling for domain 0

Make domain 0 look like all other domains wrt balloon handling:
* on system boot set memory/target to total_memory_pages (in KiB)
* on system boot set control/feature-balloon = 1

Remove the code which directly set the domain 0 memory target since this conflicts with the background ballooning code. Instead we use the API to call set_memory_dynamic_range on dom0.

Initially set the memory/target to total_memory_pages (in KiB obviously)

koushikcgit/xcp-rrdd,djs55/squeezed,koushikcgit/xcp-networkd,djs55/xcp-rrdd,johnelse/xcp-rrdd,simonjbeaumont/xcp-rrdd,koushikcgit/xcp-networkd,simonjbeaumont/xcp-rrdd,koushikcgit/xcp-rrdd,djs55/xcp-networkd,djs55/xcp-networkd,sharady/xcp-networkd,djs55/xcp-rrdd,sharady/xcp-networkd,koushikcgit/xcp-rrdd,johnelse/xcp-rrdd,robhoes/squeezed