ap_pwrseq: document event types
ap_pwrseq: document event types

BUG=b:226215993
TEST=builds
BRANCH=none

Signed-off-by: Peter Marheine <ef0b2c492edde94778d7465bfbaeed52c5be6858@chromium.org>
Change-Id: Ifaa54579bd7235f0059c26f183d0934b59974746
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3545781
Reviewed-by: Andrew McRae <44ad1424cfc8411c96d9181798ca41ae55709dfb@google.com>
Reviewed-by: Li1 Feng <0fd15d95d647a38d004d7ac9a3d0587bb1c98551@intel.com>

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