this commits:
- adds build-time test to check that no call to flash regions are done from IRAM functions
- resolves problems related to IRAM function using content in flash memory
- update heap_caps_alloc_failed to use a default function name in DRAM
when necessary instead of creating a function name variable in DRAM for
each call of heap_caps_alloc_failed. This allows to save some extra bytes
in RAM.