ANDROID: staging: android: ion: Expose ion_alloc() to kernel space

Expose ion_alloc() to kernel space clients. Users of this
function will receive a dma-buf structure for sharing
the ION buffer that was allocated.

Bug: 133508579
Test: ion-unit-tests
Change-Id: I410044127ba92a759a79c65e422b0b75b74e2159
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
Signed-off-by: Sandeep Patil <sspatil@google.com>