package/e2fsprogs: Show toolchain comment only on mmu archs

[Thomas: put BR2_USE_MMU dependency first, as suggested by Yann.]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>