mtd: devices: elm: check for hardware engine's design constraints
ELM hardware engine is used by BCH ecc-schemes for detecting and locating ECC
errors. This patch adds the following checks for ELM hardware engine:
- ELM internal buffers are of 1K,
so it cannot process data with ecc-step-size > 1K.
- ELM engine can execute upto maximum of 8 threads in parallel,
so in *page-mode* (when complete page is processed in single iteration),
ELM cannot support ecc-steps > 8.