Add a config option for llite/lloop in lustre driver, making it depends
on BLOCK to fix this better:
drivers/staging/lustre/lustre/fid/../include/linux/lustre_compat25.h:117:2:
error: implicit declaration of function ‘unregister_blkdev'
Also, remove the wrapper ll_unregister_blkdev which depends on BLOCK in
the header and just call unregister_blkdev in lloop.c based on Peng Tao's
comment. Drop the redundant dependency on STAGING for LUSTRE_FS, remove
some unnecessary jdb header files which depends on BLOCK btw.