ion: convert map_kernel to return ERR_PTR

ion is going to stop accepting NULL as an error value, use ERR_PTR.

Change-Id: I030e8b72138904e38a4a5d225beaaa98427651fb
Signed-off-by: Colin Cross <ccross@android.com>
ion: remove IS_ERR_OR_NULL

IS_ERR_OR_NULL is often part of a bad pattern that can accidentally
return 0 on error:
if (IS_ERR_OR_NULL(ptr))
    return PTR_ERR(ptr);

It also usually means that the errors of a function are not well
defined.  Replace all uses in ion.c by ensure that the return
type of any function in ion is an ERR_PTR.

Specify that the expected return value from map_kernel or map_dma
heap ops is ERR_PTR, and warn if a heap returns NULL.

Change-Id: I6e7ea0d2e62fa08d4e372a7ef6da649f7a62289c
Signed-off-by: Colin Cross <ccross@android.com>
ion: replace userspace handle cookies with idr

Userspace handles should not leak kernel virtual addresses to
userspace.  They have to be validated by looking them up in an
rbtree anyways, so replace them with an idr and validate them
by using idr_find to convert the id number to the struct
ion_handle pointer.

Change-Id: Iab5667ba6f3a73256fec3949b23a9a6f8e14a283
Signed-off-by: Colin Cross <ccross@android.com>
ion: index client->handles rbtree by buffer

The only remaining users of the client->handles rbtree are
iterating through it like a list.  Keep the rbtree, but change
its index to be the buffer address instead of the handle address,
which makes ion_handle_lookup a fast rbtree search.

Change-Id: Ie7d974b3a5d9831c0d664de85ddae8db3c3abdf9
Signed-off-by: Colin Cross <ccross@android.com>