xen/arm: allocate static shared memory to a specific owner domain

xen/arm: allocate static shared memory to a specific owner domain

If owner property is defined, then owner domain of a static shared memory
region is not the default dom_io anymore, but a specific domain.

This commit implements allocating static shared memory to a specific domain
when owner property is defined.

Coding flow for dealing borrower domain will be introduced later in the
following commits.

Signed-off-by: Penny Zheng <penny.zheng@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>