driver: espi: mchp: eSPI OOB driver does not support callbacks for incoming OOB messages from eSPI master.

[AdiIntel]

Describe the bug
Current eSPI driver allows to transmit & receive OOB messages with explicit function calls.
Driver should also allow to add callbacks to support incoming OOB messages initiated from eSPI master, so that slave (EC) doesn't have to keep polling for it always.
When the slave shows OOB status as free, then only master can send the OOB message. For this, OOB status should also be set as free always with callback set.

To Reproduce
Steps to reproduce the behavior:

1. Use eSPI driver sample code, and send an OOB message.
2. OOB status fields can be seen with Acute analyzer logs.

Expected behavior
eSPI OOB channel status should be seen as free in Acute log.
eSPI slave (EC) driver should allow incoming message handlers.

Impact
With CSME master, incoming OOB messages won't be handled.

Environment (please complete the following information):

• Toolchain (e.g Zephyr SDK, ...)

[github-actions]

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