sparc: use vmemmap_populate_hugepages for vmemmap_populate

Change sparc's implementation of vmemmap_populate() using
vmemmap_populate_hugepages() to streamline the code. Another benefit is
that it allows us to eliminate the external declarations of
vmemmap_p?d_populate functions and convert them to static functions.

Since vmemmap_populate_hugepages may fallback to vmemmap_populate-
_basepages, which differs from sparc's original implementation. During
the v1 discussion with Mike Rapoport, sparc uses base pages in the kernel
page tables, so it should be able to use them in vmemmap as well.
Consequently, no additional special handling is required.

1. In the SPARC architecture, reimplement vmemmap_populate using
vmemmap_populate_hugepages.

2. Allow the SPARC arch to fallback to vmemmap_populate_basepages(),
when vmemmap_alloc_block returns NULL.

Link: https://lkml.kernel.org/r/20260201063532.44807-2-pilgrimtao@gmail.com
Signed-off-by: Chengkaitao <chengkaitao@kylinos.cn>
Tested-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Andreas Larsson <andreas@gaisler.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>