zephyr: docs: add TCPC documentation
zephyr: docs: add TCPC documentation

Document the TCPC Kconfig.tcpm options

BUG=b:208437225
TEST=Browse doc in gerrit
BRANCH=main

Signed-off-by: Sam Hurst <500b4cddcd66abe3fe333e92c4c95d7f41e62e4e@google.com>
Change-Id: I7e917d823dbb18208257d84d6b441e59b19228e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3811790
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Commit-Queue: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>

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