valgrind: improve mips support

We have to remove the FPU check, it will run in an endless loop on LEDE
when compile without FPU emulation support.
The second patch fixes this problem: valgrind: mmap(0x400000, 303104)
failed in UME with error 22 (Invalid argument).

valgrind still does not support mips16, build LEDE without mips16 support.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>