drivers/espi: Add structure for evt_data in peripheral PVT events

Introduce a new bit field structure "espi_evt_data_pvt" to represent
the evt_data field in PVT IO related eSPI peripheral events.

With this change, callback functions handling eSPI events can extract
both the data and its associated type from evt_data.

Signed-off-by: Tim Lin <tim2.lin@ite.corp-partner.google.com>

include/zephyr/drivers/espi.h

@@ -343,6 +343,15 @@ struct espi_evt_data_acpi {
 	uint32_t reserved:16;
 };
 
+/**
+ * @brief Bit field definition of evt_data in struct espi_event for PVT.
+ */
+struct espi_evt_data_pvt {
+	uint32_t type: 8;
+	uint32_t data: 8;
+	uint32_t reserved: 16;
+};
+
 /**
  * @brief eSPI event
  */