firmware: arm_scmi: Publish channel state before callbacks

In the Linux kernel, the following vulnerability has been resolved:

firmware: arm_scmi: Publish channel state before callbacks

Transport setup can enable callbacks before the setup routine returns.
mailbox_chan_setup() registers the mailbox client with
mbox_request_channel(), and the mailbox controller startup path can enable
interrupt delivery before SCMI mailbox channel state has been published.
Similarly, smc_chan_setup() requests the optional A2P completion IRQ before
the SMC transport has made its cinfo pointer visible.

If a pending or spurious callback fires in those windows, the transport RX
callback can dereference a NULL transport cinfo pointer. Publishing only
the transport-private pointer is not sufficient either: an early callback
can enter the SCMI core before scmi_chan_setup() has assigned
cinfo->handle.
The core derives scmi_info from cinfo->handle in the RX path, so a NULL
handle can still fault even when the transport-private cinfo is valid.

Assign cinfo->handle before invoking the transport setup callback. Publish
the mailbox and SMC transport-private channel state before requesting the
mailbox channels or IRQ, and clear the early-published pointers again on
setup failure. Also unwind mailbox setup devres resources on failure so an
optional RX setup error that is ignored by the core does not leave stale
transport state behind.