tablet-mode: Fix header file guard and API definitions
tablet-mode: Fix header file guard and API definitions

This patch adds a usual inclusion guard (#ifdef __CROS_EC_*_H) and
fixes API descriptions.

Signed-off-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

BUG=none
BRANCH=none
TEST=buildall

Change-Id: I96149cfe76cff7ab85be4785252a600b565e4a92
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1696913
Reviewed-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Commit-Queue: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Tested-by: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>
Auto-Submit: Daisuke Nojiri <fd5f93af191bf7e8f73ea71cc3c0f66b41b1dd49@chromium.org>

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