ec/google/chromeec: Split wait-loop for DP and HPD flags

Split wait-loop for DP and HPD flags as below -
- google_chromeec_wait_for_hpd
- google_chromeec_wait_for_dp_mode_entry

BUG=b:247670186
TEST=Verify display over TCSS and its impact on boot time for
google/rex

Signed-off-by: Kapil Porwal <kapilporwal@google.com>
Change-Id: I3e565d6134f6433930916071e94d56d92dc6cb06
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76370
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/device/usbc_mux.h

@@ -54,6 +54,15 @@ struct usbc_dp_ops {
 	 */
 	int (*enter_dp_mode)(int port);
 
+	/*
+	 * Wait up to `timeout_ms` for DP mode entry on a given port.
+	 *
+	 * Return value:
+	 * -1 = timeout
+	 *  0 = success
+	 */
+	int (*wait_for_dp_mode_entry)(int port, long timeout_ms);
+
 	/*
 	 * Wait up to `timeout_ms` for HPD on a given port.
 	 *