[AMDGPU] Allow some modifiers on VOP3B instructions

[AMDGPU] Allow some modifiers on VOP3B instructions

V_DIV_SCALE_F32/F64 are VOP3B encoded so they can't use the ABS src
modifier, but they can still use NEG and the usual output modifiers.

This partially reverts 3b99f12a4e6f "AMDGPU: Remove modifiers from v_div_scale_*".

Differential Revision: https://reviews.llvm.org/D90296