lib/vboot_kernel: Log speed at which kernel was loaded
lib/vboot_kernel: Log speed at which kernel was loaded

This makes it easy to spot the speed at which the eMMC controller is
running.

vb2_load_partition: read 8419 KB in 48 ms at 174342 KB/s.

The calculation looks a little funky because I wanted to perform all
multiplications before the division to avoid losing any precision.

BRANCH=grunt
BUG=b:122244718
TEST=Verified it on grunt

Change-Id: I5fac584994bc478bfb27cbd4e2ea34af0be7f1d9
Signed-off-by: Raul E Rangel <9a9c998e11a2655b1de9a05eeeef5f710c0dc7ed@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/1661366
Reviewed-by: Julius Werner <4d12f06cff3725783b352157673a720bc67c4afe@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot