[AVR] Expand shifts of all types except int8 and int16

Currently our AVRShiftExpand pass expands only 32-bit shifts, with the
assumption that other kinds of shifts (e.g. 64-bit ones) are
automatically reduced to 8-bit ones by LLVM during ISel.

However this is not always true and causes problems in the rust-lang runtime.

This commit changes the logic a bit, so that instead of expanding only
32-bit shifts, we expand shifts of all types except 8-bit and 16-bit.

This is not the most optimal solution, because 64-bit shifts can be
expanded to 32-bit shifts which has been deeply optimized.

I've checked the generated code using rustc + simavr, and all shifts
seem to behave correctly.

Spotted in the wild in rustc:
https://github.com/rust-lang/compiler-builtins/issues/523
https://github.com/rust-lang/rust/issues/112140

Reviewed By: benshi001

Differential Revision: https://reviews.llvm.org/D154785