x86: Always inline task_size_max()

Fix:

  vmlinux.o: warning: objtool: handle_bug()+0x10: call to task_size_max() leaves .noinstr.text section

When #UD isn't a BUG, we shouldn't violate noinstr (we'll still
probably die, but that's another story).

Fixes: 025768a9

 ("x86/cpu: Use alternative to generate the TASK_SIZE_MAX constant")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210621120120.682468274@infradead.org