Add protected region

Add protection region value and check it against base address.

As minimum, the protected region should be the first 8 bytes, following the manual recommendation.
It might be interesting more restriction than that, due to the usage of ushm for simulated motors.

Start by locating the C code that handles the base address and assigns data into the Power PMAC buffer. Read how the buffer address is currently checked, then define the protected region as the first 8 bytes and verify that the base address cannot overlap it. Confirm the behavior with the available project checks, though no test file is named in the issue.

Written by the indexing model from the issue text.