ec_commands: Add structs for host command protocol V4
ec_commands: Add structs for host command protocol V4

This only adds the structs for V4 packets.  Host command support for
them is coming in a subsequent CL.  V3 packets will continue to be
supported for a while, until all sides support V4.

BUG=chromium:787159
BRANCH=none
TEST=make -j runtests

Change-Id: I7e188a063d8ed60c85f3b8359959c424e3ccd1d9
Signed-off-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/780452
Reviewed-by: Nicolas Boichat <f3daba1cdc403799935674d3cd4b0e5bd1804232@chromium.org>

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