API: espi: Add API for Enhanced Serial Peripheral Interface

    This API defines following call for eSPI bus drivers

    - espi_set_config
    - espi_get_channel_status
    - espi_send_read_request
    - espi_send_write_request
    - espi_send_vwire
    - espi_receive_vwire
    - espi_send_oob
    - espi_receive_oob
    - espi_flash_read
    - espi_flash_write
    - espi_flash_erase

Signed-off-by: Jose Alberto Meza <jose.a.meza.arellano@intel.com>