Configuration of EP methods

[dccutrig]

Currently EPs are supported one of two ways:

1. Using a packet layer APID (0x1880)
2. Using a specific VDIC (currently referenced at 4)

This like needs to be an either / or config so missions don't unintentionally have a hole in their security posture (e.g. not realizing VCID 4 can accept EP commands)

However, both of these options still rely on either SPI_MIX or SPI_MAX being the SPI in use.

This also further implicitly seems to enforce that SPI number is a direct mapping to an SA (atleast in my mind)