Add orphan.c to the ext4l build and fix various build issues:
- Add atomic_inc/atomic_dec macros to ext4_uboot.h
- Add s_flags member to struct super_block and SB_RDONLY constant
- Add bdev_read_only() stub function
- Add kvfree() and kvmalloc_array() to linux/slab.h
- Add stub functions for orphan.c: ext4_reserve_inode_write,
ext4_superblock_csum_set, ext4_mark_iloc_dirty, ext4_truncate,
ext4_feature_set_ok, ext4_bread
- Fix orphan.c to use U-Boot include pattern
- Remove linux/atomic.h include from buffer_head.h (types provided
by ext4_uboot.h)
- Add kunit/static_stub.h and linux/nospec.h stub headers
- Simplify seq_file.h macros
Co-developed-by: Claude Opus 4.5 <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
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