Changing PMP Grain through CLI

[iamkarthikbk]

Hi

I'm aware of the option to change the number of PMP entries using the CLI option --pmpregions=<n>. I think it would be helpful if we could also set the PMP grain in a similar fashion. I want to use spike with a pmp grain other than the default value. I went through the code base a little bit and found this function. Can we expose it to be called through the CLI ? Perhaps an option --pmpgrain=<n> ?

Writing a grain that is less than the minimum would simply be ignored based on the current framework, and all of that seems right. I would appreciate it if someone can throw some more light on this. As of this moment, in order to change the PMP grain, i'd have to do this and then rebuild spike. Please correct me if I'm wrong. Thanks in advance!

[iamkarthikbk]

If this is something the maintainers would like, I can work on this feature addition.

[jerryz123]

I think this flag would be ok to add.

Nit: it should be 'pmpgranularity'.

[iamkarthikbk]

Thanks for the comment, @jerryz123 .
Do you think my PR (#1490) does the trick?
Please let me know if I've missed something, and I'll be happy to make the change.

Changes in this PR have been compile-tested by me.