TCPMv2: Use CMD_DISCOVER_IDENT during discovery
TCPMv2: Use CMD_DISCOVER_IDENT during discovery

enum vdm_cmd is redundant with the CMD_DISCOVER_* macros in usb_pd.h and
will no longer be needed after pe_do_port_discovery is replaced. Remove
uses of enum vdm_cmd from the new VDM request states.

BUG=none
TEST=make buildall
BRANCH=none

Change-Id: I068fa3a1f9208953b18b1bf765a0adfa54ad8df0
Signed-off-by: Abe Levkoy <2e1ad7039298f93262cf06bbb457275fb3e2ecb5@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2178092
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

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