fs/Kconfig: move ext2, ext3, ext4, JBD, JBD2 out

Use fs/*/Kconfig more, which is good because everything related to one
filesystem is in one place and fs/Kconfig is quite fat.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>