staging: ion : Donnot wakeup kswapd in ion system alloc

Since ion alloc can be called by userspace,eg gralloc.
When it is called frequently, the efficiency of kswapd is
to low. And the reclaimed memory is too lower. In this way,
the kswapd can use to much cpu resources.

With 3.5GB DMA Zone and 0.5 Normal Zone.

pgsteal_kswapd_dma 9364140
pgsteal_kswapd_normal 7071043
pgscan_kswapd_dma 10428250
pgscan_kswapd_normal 37840094

With this change the reclaim ratio has greatly improved
18.9% -> 72.5%

Signed-off-by: Chen Feng <puck.chen@hisilicon.com>
Signed-off-by: Lu bing <albert.lubing@hisilicon.com>
Reviewed-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>