fix flash_cache_table allocation failures; clean up code

[dhalbert]

• Fixes Simply allocating memory causes hard crash & board freeze on code re-upload #9162

There were problems when the flash_cache_table entries could not be completely allocated. That code was made simpler. In addition there were some missing guards handling the case when the flash_cache_table itself could not be allocated.

I made some #defines that simplified some size values that were used multiple places.

release_ram_cache() was moved up in declaration order so it could be newly called from another routine. It now handles cleanup of an only partially-allocated flash_cache_table.

[tannewt]

Looks good! Thanks!

Did you find this code in any ports/<port>/supervisor/internal_flash.c?

[dhalbert]

Did you find this code in any ports/<port>/supervisor/internal_flash.c?

I didn't look. I will!