drivers: samples: espi: Adjust terms per eSPI specification 1.5

Replace CONFIG_ESPI_SLAVE by CONFIG_ESPI_TARGET
Replace CONFIG_ESPI_SAF by CONFIG_ESPI_TAF
Replace ESPI_BUS_SAF_NOTIFICATION with ESPI_TAF_BUS_NOTIFICATION in API

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