Some refactoring of domain creation/destruction.

Some refactoring of domain creation/destruction.

Interface name changes:
1. do_createdomain -> domain_create

2. domain_destruct -> domain_destroy

Arch-specific changes:
1. arch_do_createdomain -> arch_domain_create
This function now takes a domain pointer, not a VCPU
pointer! Initialisation of VCPU0 must happen in
alloc_vcpu_struct().

2. free_perdomain_pt -> arch_domain_destroy
This function must undo the work of arch_domain_create

TODO: arch_domain_create() refactoring is not completed
for ia64.

Signed-off-by: Keir Fraser <keir@xensource.com>