include/linux/pgtable.h: convert arch_enter_lazy_mmu_mode() and friends to static inlines

commit c519c3c ("mm/kasan: avoid lazy MMU mode hazards") introduced
the use of arch_enter_lazy_mmu_mode(), which results in the compiler
complaining about "statement has no effect", when
__HAVE_ARCH_LAZY_MMU_MODE is not defined in include/linux/pgtable.h

The exact warning/error is:

In file included from ./include/linux/kasan.h:37,
                 from mm/kasan/shadow.c:14:
mm/kasan/shadow.c: In function kasan_populate_vmalloc_pte:
./include/linux/pgtable.h:247:41: error: statement with no effect [-Werror=unused-value]
  247 | #define arch_enter_lazy_mmu_mode()      (LAZY_MMU_DEFAULT)
      |                                         ^
mm/kasan/shadow.c:322:9: note: in expansion of macro arch_enter_lazy_mmu_mode>   322 |         arch_enter_lazy_mmu_mode();
     |         ^~~~~~~~~~~~~~~~~~~~~~~~

switching these "functions" to static inlines fixes this up.

Fixes: c519c3c ("mm/kasan: avoid lazy MMU mode hazards") 
Reported-by: Balbir Singh <balbirs@nvidia.com>
Closes: https://lkml.kernel.org/r/20250912235515.367061-1-balbirs@nvidia.com
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: akpm00

include/linux/pgtable.h

@@ -232,9 +232,9 @@ static inline int pmd_dirty(pmd_t pmd)
  * and the mode cannot be used in interrupt context.
  */
 #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
-#define arch_enter_lazy_mmu_mode()	do {} while (0)
-#define arch_leave_lazy_mmu_mode()	do {} while (0)
-#define arch_flush_lazy_mmu_mode()	do {} while (0)
+static inline void arch_enter_lazy_mmu_mode(void) {}
+static inline void arch_leave_lazy_mmu_mode(void) {}
+static inline void arch_flush_lazy_mmu_mode(void) {}
 #endif
 
 #ifndef pte_batch_hint