changes to support provisional logs

[mgudaram]

Provisional logs store logs until VMM enables memory logging and copies these logs into the memory area. Provisional logs would be 4KB circular buffer per vCPU.

[jyao1]

I am OK with this change. May I know what kind of test you have run to ensure the code is correct?

[mgudaram]

Hi Jiewen,

I have added few unit-test cases in this PR to test the basic feature functionality (new feature also uses the same function entrylog as logging but with different memory area, so all the unit testcases relevant for logging cornercases will verify provisionallog circular buffer as well),
test_provisional_entrylog
test_provisional_and_entrylog_combined

Also, I booted the MigTD (w/o proviosional log vs w/), exposed memory area from VMM and we can now see the logs prior to enablelogarea request with new feature. PFA the image of windbg

w/ provisional logs enabled, earlier boot logs are copied and exposed in shared memory area during enablelogarea

w/o provisional logs, only logs after enablelogarea are visible in memory area

Thanks,
Meghana