mm: don't allow deferred pages with NEED_PER_CPU_KM

It is unsafe to do virtual to physical translations before mm_init() is
called if struct page is needed in order to determine the memory section
number (see SECTION_IN_PAGE_FLAGS).  This is because only in mm_init()
we initialize struct pages for all the allocated memory when deferred
struct pages are used.

My recent fix in commit c9e97a19 ("mm: initialize pages on demand
during boot") exposed this problem, because it greatly reduced number of
pages that are initialized before mm_init(), but the problem existed
even before my fix, as Fengguang Wu found.

Below is a more detailed explanation of the problem.

We initialize struct pages in four places:

1. Early in boot a small set of struct pages is initialized to fill the
   first section, and lower zones.

2. During mm_init() we initialize "struct pages" for all the memory that
   is allocated, i.e reserved in memblock.

3. Using on-demand logic when pages are allocated after mm_init call
   (when mem...

mm/Kconfig

@@ -636,6 +636,7 @@ config DEFERRED_STRUCT_PAGE_INIT
 	default n
 	depends on NO_BOOTMEM
 	depends on !FLATMEM
+	depends on !NEED_PER_CPU_KM
 	help
 	  Ordinarily all struct pages are initialised during early boot in a
 	  single thread. On very large machines this can take a considerable