TCPMv2: Update BIST comments
TCPMv2: Update BIST comments

Correctly cite PD 3.0 spec.

BUG=none
TEST=make buildall
BRANCH=none

Signed-off-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>
Change-Id: I26de0d34e99291d5320051ff47f0fc7c5d84b4b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2545666
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec