Modify ion to use new definition of ALLOC ioctl argument

Also add ion_alloc_fd helper for when you only want a filedescriptor
and know you won't need to access this handle again by its ion_handle

Signed-off-by: Rebecca Schultz Zavin <rebecca@android.com>

Change-Id: Ia4bae22946b0078084b62f5447fecbf261dfaa83