bsp/tms570: disable huge memory demanding tests for internal RAM build variant.

BSP completes build with tests and debug enabled for all three variants now

  tms570ls3137_hdk
  tms570ls3137_hdk_intram
  tms570ls3137_hdk_sdram

Even that all enabled tests builds for internal RAM variant, many
of them are expected to fail on hardware because whole tests
including code, data and runtime work area demands has to fit
into 256 kB of RAM.