gpu: ion: make sure all clients are exposed in debugfs

Currently, if multiple Ion clients are created with the same name, only
the first one shows up in debugfs. Rectify this by adding a
monotonically-increasing serial number to the debug names of Ion
clients.

CRs-Fixed: 566001
Change-Id: I000e45055d5029c7bccd88c36b238736929da3a5
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
gpu: ion: Support probe deferal for client creation

Ion is treated like any other device in the system. Clients
may try to initialize before Ion is setup. If the Ion driver
has not yet probed, return -EPROBE_DEFER to try again later.
Since the flow is being restructured to support probe deferal,
also include some better error handling for when Ion returns
an error while probing.

Change-Id: I7ee6dde2c837fba8bba0ba4aaddee3af37b2fec1
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>