Fixed for updated SMC control, SPI loading in release

- The renode model of the control block was changed to match with the
  RTL version, so update load_sel4 accordingly.
- Instead of checking whether we run on FPGA to decide whether to load
  from SPI, check whether we're a debug or release build:
  - On debug builds, load from the memory mapped binaries (since debug
    binaries are enormous, and renode SPI isn't that fast)
  - On release builds, load from SPI (and since release builds don't fit
    in FPGA, this also means that FPGA always loads from SPI).

Change-Id: I09a50e603e11c020cb6004a921709a44fac88802