samples: exclude mec15xxevb_assy6853 in espi sample when sanitycheck

ESPI is supported in MEC15 chips but similar to PECI, I2C, eSPI bus
testing requires another device to act as eSPI host.
While this sample can be run in EVB the HW connection to a eSPI host
(Intel RVP) is not documented/supported.

Mark as not supported in that HW only in Modular card
(which setup is documented)

Also remove duplicate definition of the "depends_on: espi"
in the end of the sample.yaml file

Signed-off-by: Maksim Masalski <maksim.masalski@intel.com>