[kernel] Set framebuffer to write-combining

Several changes were needed to make this work:

- Update the page_table::flags to understand memory caching types
- Set up the PAT MSR to add the WC option
- Make page-offset area mapped as WT
- Add all the MTRR and PAT MSRs, and log the MTRRs for verification
- Add a vm_area flag for write_combining

src/kernel/scheduler.cpp

@@ -141,7 +141,7 @@ load_process_image(uintptr_t phys, uintptr_t virt, size_t bytes, TCB *tcb)
 
 	// Crazypants framebuffer part
 	if (fb) {
-		vma = new vm_area_open(fb->size, space, vm_flags::write|vm_flags::mmio);
+		vma = new vm_area_open(fb->size, space, vm_flags::write|vm_flags::mmio|vm_flags::write_combine);
 		space.add(0x100000000, vma);
 		vma->commit(fb->phys_addr, 0, memory::page_count(fb->size));
 	}