Heap init code improvements and updates

[mhightower83]

Moved secondary heap init code to flash.

 External -24 IRAM, +32 IROM IRAM -76 IRAM, +64 IROM 

General updates to umm_init call path and defines to better align with upstream. Name changes: UMM_INIT_HEAP with UMM_CHECK_INITIALIZED, umm_init_stage_2 with _umm_init_heap, and umm_init_common with umm_init_heap.

Add file umm_cfgport.h to hold port-specific values. Stay focused on heap initialization only move-related defines.

Improved comments.

Created a wrapper function for running pre-SDK code from flash.
Updated hwdt_app_entry to use it.

Update umm_init with the option to run from ICACHE.
Added build define UMM_INIT_USE_ICACHE to move umm_init call path to flash.
Added build define UMM_INIT_USE_IRAM to move umm_init call path back to IRAM.
Using ICACHE frees up 160 bytes of IRAM at a cost of 208 bytes of IROM.

Defaults to no change, umm_init call path will be in IRAM.
Defaults with umm_init call path in ICACHE.

[d-a-v]

Defaults to no change, umm_init call path will be in IRAM.

Would it be more efficient to change default settings ?

Other than that, LGTM and thanks !

[mhightower83]

@d-a-v I was being over-cautious. The experience we have with using switching cache on and off before the SDK initializes is with HWDT Stack Dump, which for me has worked fine without issue. I don't know how often it gets used. I also used it in one of the methods in my "ideas for config erase" PR. So I played it safe and left it as an option to turn on.

Hmm, if we have a while before the next dot release and you guys feel comfortable with the change, I could switch the default around?

[d-a-v]

Hmm, if we have a while before the next dot release and you guys feel comfortable with the change, I could switch the default around?

We think it is OK to go this way !

[d-a-v]

Thanks!