misctrl: read message, incl 16kb flag

Add a misctrl specific message with its first use.
Future platform flags can go here for any purpose,
without needing to add separate utilities.

Check if a device has ever been in 16KB before so that
we are able to tell if 16KB causes any issues.

Bug: 317262681
Test: boot, bugreport
Change-Id: I21299ded1520020768462950713cbe49ca3c438f