mm: Inform KASAN when allocating pages during isolation

kasan_alloc_pages() should be called alongside kernel_map_pages() to
prevent splats when CONFIG_KASAN is enabled.

This is a greatly simplified version of
commit 46f24fd857b37bb86ddd5d0ac3d194e984dfdf1c
("mm/page_alloc: introduce post allocation processing on page allocator")
which solve the same problem on later kernel versions.

Change-Id: Ib60d079a4d8685e781624bb1403b2a3060e31d27
Signed-off-by: Patrick Daly <pdaly@codeaurora.org>