Add support for extent-moving for write operations.
Use ext4_uboot.h compatibility layer and add stubs for:
- down_write_nested - forwards to down_write
- filemap_release_folio, IS_SWAPFILE, PAGE_MASK
- lock_two_nondirectories, unlock_two_nondirectories
Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>