scmi: Add new SCMI interfaces for init and message processing

[cristian.marussi_arm.com]

Summary

Introduce a couple of new SCMI interface methods to allow centralized
initialization of transport-specific features and a couple of methods
to handle message reception from the SCMI core.

Move SCMI SMT related calls out of the core common SCMI code into the
transport specific layers Mailbox/SMC.

Make SCMI Mailbox/SMC transports use the new interface methods for
initialization and message reception.

Tested on: ARM Morello Board
Sponsored by: Arm Ltd

[andrew]

The attach and detach functions that just call smci_attach and smci_detach could be removed. If a driver doesn't implement a method, but the parent does then the parent implementation will be used.

[cristian.marussi_arm.com]

In D43044#989468, @andrew wrote:

The attach and detach functions that just call smci_attach and smci_detach could be removed. If a driver doesn't implement a method, but the parent does then the parent implementation will be used.

Thanks, did not know that, I'll fix.

[cristian.marussi_arm.com]

Removed needless empty interface methods

Removed from SMC/MAILBOX the interface methods that just simply called
the parent scmi_attach()/scmi_detach()

[andrew]

sys/dev/firmware/arm/scmi.c

147

I think this can stay static

[cristian.marussi_arm.com]

sys/dev/firmware/arm/scmi.c

147

I'll do. Thanks for ponting out.

[cristian.marussi_arm.com]

Made scmi_detach static

scmi_detach is not needed anywhere else outside so made it static.