nfs-utils: needs mmu

Fix below build error:

mountd-mountd.o: In function `main':
mountd.c:(.text+0x1264): undefined reference to `fork'
mountd.c:(.text+0x1320): undefined reference to `fork'
mountd-rmtab.o: In function `ha_callout':
rmtab.c:(.text+0xa8): undefined reference to `fork'
collect2: ld returned 1 exit status
make[3]: *** [mountd] Error 1

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>