Updated comment regarding clobbers on the SBI call.
Tweak a boot time print of SBI version.
Add a commented out line to the do-qemuriscv to assist in dumping future
device trees.
-Fix plic driver to handle machine vs supervisor mode
-Add switch to scripts/do-qemuriscv to run in supervisor mode (with OpenSBI)
-Use the FDT to detect the number of cpus and size of memory
Very little needed to port except to conditionalize some assembly in the
context switch and exception code. Mostly needed to move build system
stuff around and add a new project.
