luvi: build for the right MIPS endianness

luvi: build for the right MIPS endianness

Otherwise it will cause build failures like this one:

[100%] Linking C executable luvi
/home/buildroot/autobuild/run/instance-2/output/host/opt/ext-toolchain/bin/../lib/gcc/mipsel-buildroot-linux-gnu/5.2.0/../../../../mipsel-buildroot-linux-gnu/bin/ld:
jitted_tmp/src/lua/init.lua_luvi_generated.o: compiled for a big endian
system and target is little endian

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>