uclibc: Add UCLIBC_MMU_CONFIG to UCLIBC_SETUP_DOT_CONFIG

commit c798bec2 "uclibc: set MMU usage accordingly" defines UCLIBC_MMU_CONFIG,
but forgot adding it to UCLIBC_SETUP_DOT_CONFIG. Fix it.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>