Add NDK Interface (NIMU) module to NDK sysconfig

The NDK needs to have its own NIMU module to generate the NIMU_DEVICE_TABLE for the user. This generation is currently being done by the EMAC SysConfig module (part of TI-DRIVERS), but is better architected when moved into the NDK's SysConfig.

The NIMU module should allow the user to select from a list of possible "interfaces" based on the device being configured. We will also need to account for NIMU PPP interfaces.

The user should also be allowed to place a custom NIMU interface by naming their own init function. This function would have to be written by the user and placed in their app source code.