Update ext4_uboot.h to include the new linux headers instead of
defining types locally. Remove duplicate definitions of:
- MAX_JIFFY_OFFSET (now in linux/jiffies.h)
- BDEVNAME_SIZE (now in linux/blkdev.h)
- rwlock_t (now in linux/spinlock.h)
Remove rwlock_init() stub from stub.c since it's now a macro.
Signed-off-by: Simon Glass <simon.glass@canonical.com>