drivers: versal: mbox: Rework

- Offer a generic IPI/Mailbox API in versal_mbox.c and ...
- ... provide the default IPI channel to the PMC for other drivers in
versal_pmc.c .

- Improve performance

drivers: versal: mbox: Rework

- Offer a generic IPI/Mailbox API in versal_mbox.c and ...
- ... provide the default IPI channel to the PMC for other drivers in
versal_pmc.c .

- Improve performance by doing notification by direct, memory-mapped
register access instead of doing it through the SecureMonitor.

Largely based on previous work by
Jeremie Corbier <jeremie.corbier@provenrun.com>.

Signed-off-by: Joachim Foerster <joachim.foerster@missinglinkelectronics.com>
Reviewed-by: Nathan Menhorn <nathan.menhorn@amd.com>
Tested-by: Nathan Menhorn <nathan.menhorn@amd.com>
Reviewed-by: Sean McGinn <sean.mcginn@amd.com>
Reviewed-by: Lucas Kiker <lucas.kiker@amd.com>
Reviewed-by: Sindhu Raveendra <Sindhu.Raveendra@amd.com>
Reviewed-by: Clemens Nasenberg <clemens.nasenberg@amd.com>
Reviewed-by: Jorge Ramirez-Ortiz <jorge.ramirez@oss.qualcomm.com>

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