mm: refactor vma_map_pages to use vm_insert_pages

vma_map_pages currently calls vm_insert_page on each individual page in
the mapping, which creates significant overhead because we are repeatedly
spinlocking. Instead, we should batch insert pages using vm_insert_pages,
which amortizes the cost of the spinlock.

Tested through watching hardware accelerated video on a MTK ChromeOS
device. This particular path maps both a V4L2 buffer and a GEM allocated
buffer into userspace and converts the contents from one pixel format to
another. Both vb2_mmap() and mtk_gem_object_mmap() exercise this pathway.

Link: https://lkml.kernel.org/r/20260128225648.2938636-1-greenjustin@chromium.org
Signed-off-by: Justin Green <greenjustin@chromium.org>
Acked-by: Brian Geffon <bgeffon@google.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Arjun Roy <arjunroy@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>