gpu: ion: Fix several issues with page pool

Split out low and high mem pages so they are correctly reported
when the shrinker is called.
Fix potential deadlock caused by holding the page pool lock while
allocationg and also needing that lock from the shrink function

Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>
[jstultz: modified patch to apply to staging directory]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>