mm/vmalloc: Enter lazy mmu mode while manipulating vmalloc ptes

Wrap vmalloc's pte table manipulation loops with
arch_enter_lazy_mmu_mode() / arch_leave_lazy_mmu_mode(). This provides
the arch code with the opportunity to optimize the pte manipulations.

Note that vmap_pfn() already uses lazy mmu mode since it delegates to
apply_to_page_range() which enters lazy mmu mode for both user and
kernel mappings.

These hooks will shortly be used by arm64 to improve vmalloc
performance.

Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>