Software support for PMS module.
Allows controlled memory access to IRAM (R/W/X) and DRAM0 (R/W)
On/locked by default, configurable in Kconfig (esp_system)
Closes https://jira.espressif.com:8443/browse/IDF-2092
These definitions have ended up being chip specific. Moving them into
respective soc_memory_layout.c makes the whole picture of memory
regions easier to see, and also makes adding support for new chips
easier.