mm: make is_vmalloc_addr lockless

is_vmalloc_addr currently takes the vmap_area_lock and walks
the list of vmalloc areas to determine if an address is actually
a vmalloc address. Unfortunately, the current locking structure
with vmap_area_lock does not disable irqs which means that it may
be possible to recusively take the vmap_area_lock if an irq occurs
while walking the tree list. Considering the list of possible
vmalloc vs. not vmalloc ranges is not going to change after bootup,
skip the tree walking and just keep a bitmap of which virtual
addresses are set aside for vmalloc and which are not.

Change-Id: I0c159e09dc17b5c6641d08dcf630e6116b991cd5
CRs-Fixed: 591797
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>