uprobes/x86: Fix is_64bit_mm() with CONFIG_X86_X32
is_64bit_mm() assumes that mm->context.ia32_compat means the 32-bit
instruction set, this is not true if the task is TIF_X32.
Change set_personality_ia32() to initialize mm->context.ia32_compat
by TIF_X32 or TIF_IA32 instead of 1. This allows to fix is_64bit_mm()
without affecting other users, they all treat ia32_compat as "bool".
TIF_ in ->ia32_compat looks a bit strange, but this is grep-friendly
and avoids the new define's.