[AVR] Do not use divmod calls for bigger integers

The avr-libc provides *divmodqi4, *divmodhi4, and *divmodsi4 functions,
but does not provide a *divmoddi4. Instead it provides regular *divdi3
and *moddi3 functions.

Note that avr-libc doesn't support *divti3 or *modti3 for 128-bit
integer manipulation.

Source:
https://github.com/gcc-mirror/gcc/blob/releases/gcc-5.4.0/libgcc/config/avr/lib1funcs.S

Differential Revision: https://reviews.llvm.org/D78437