xen/arm: introduce acquire_staticmem_pages and acquire_domstatic_pages

xen/arm: introduce acquire_staticmem_pages and acquire_domstatic_pages

New function acquire_staticmem_pages aims to acquire nr_mfns contiguous pages
of static memory, starting at #smfn. And it is the equivalent of
alloc_heap_pages for static memory.

For each page, it shall check if the page is reserved(PGC_reserved)
and free. It shall also do a set of necessary initialization, which are
mostly the same ones in alloc_heap_pages, like, following the same
cache-coherency policy and turning page status into PGC_state_inuse, etc.

New function acquire_domstatic_pages is the equivalent of alloc_domheap_pages
for static memory, and it is to acquire nr_mfns contiguous pages of
static memory and assign them to one specific domain.

It uses acquire_staticmem_pages to acquire nr_mfns pages of static memory.
Then on success, it will use assign_pages to assign those pages to one
specific domain.

In order to differentiate pages of static memory from those allocated from
heap, this patch introduces a new page flag PGC_reserved, then mark pages of
static memory PGC_reserved when initializing them.

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