[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/objects/vm_area.h

@@ -29,6 +29,7 @@ enum class vm_flags : uint32_t
 	huge_pages      = 0x00000200,
 
 	mmio            = 0x00010000,
+	write_combine   = 0x00020000,
 
 	user_mask       = 0x0000ffff  ///< flags allowed via syscall
 };