include/config.h: Clarify intent of local entropy
include/config.h: Clarify intent of local entropy

Clarify the meaning of defining:
CONFIG_ROLLBACK_SECRET_LOCAL_ENTROPY_SIZE

This is only meant to add a little bit of extra entropy, when the
hardware lacks a random number generator (otherwise, the strong
entropy can be directly added to the secret, using
rollback_add_entropy).

BRANCH=none
BUG=b:111190988
TEST=none

Change-Id: Ife77f65ccdf8c36c8143b8d0a68526ad3c773c90
Signed-off-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1132825
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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