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

commit c519c3c0a113 ("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: c519c3c0a113 ("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>