espi: it8xxx2: enable configuration of Chromebook

This enables the below configuration so the AP and EC are able to
communicate over eSPI:

CONFIG_ESPI_PERIPHERAL_EC_HOST_CMD
CONFIG_ESPI_PERIPHERAL_ACPI_SHM_REGION
CONFIG_ESPI_PERIPHERAL_CUSTOM_OPCODE

Signed-off-by: Dino Li <Dino.Li@ite.com.tw>
8 files changed