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: 025768a ("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

arch/x86/include/asm/page_64.h

@@ -75,7 +75,7 @@ void copy_page(void *to, void *from);
  *
  * With page table isolation enabled, we map the LDT in ... [stay tuned]
  */
-static inline unsigned long task_size_max(void)
+static __always_inline unsigned long task_size_max(void)
 {
 	unsigned long ret;