Introduced in 97e3542947.
The previous commit frees the IRAM part when single core, but doesn't
change the memory layout functions. The unit test mallocs IRAM memory
from the heap, accidently into the new-released region, which doesn't
match the memory layout function.
This commit update the memory layout function to fix this.
No longer necessary to keep all reserved addresses in 'soc'.
Means 'soc' does not need to know about 'bt', for example.
Also means that Bluetooth can be enabled in config without any memory being reserved for BT
controller. Only if code calling the BT controller is linked in, will this memory be reserved...
