gpu: ion: optimize system heap for non fault buffers

If a buffer's user mappings are not going to be faulted
in it need not be allocated page wise.  We can optimize
this common case by allocating an sglist of larger chunks
rather than creating an entry for each page in the
allocation.

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>