haiku_loader.riscv: update

* Moved machine mode code from kernel.
* Added MMU page table generation.
* Added QEMU ramfb video driver.

Change-Id: Icd67cd2e8dbf2b568d81ab8dd0d6127ca3cd97a8
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4302
Reviewed-by: Alex von Gluck IV <kallisti5@unixzen.com>