In the past, we have struggled with long delays while reading data from disk in
real mode, leading to big boot times (not that they are totally gone). For that
reason, it is useful to know how much time is being spent in that process.  As
unstable and broken the TSC is, it is pretty much our only ally for that.

What I am proposing in this patch, is that we take timings from key states of
the bootloader, and pass that to main loader. We will do that by adding some
space at the end of the multiboot_info structure, so that we can pass some
fields to it. Right now, we are using 16 bytes so we can pass 2 64-bit tsc
reads.

Signed-off-by: Glauber Costa <glommer@cloudius-systems.com>
Reviewed-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>