Beken deep sleep missing

[Stoatwblr]

Describe the enhancement

Libretiny has had deep sleep support for BK7321N for a while and there are numerous battery powered devices using this particular CPU which need it (On average a pair of AA cells last less than a day without sleep modes)

szupi-ipuzs produced a PR addressing this issue a while back but it was never implemented. Trying to use it as an external (lt_deep_sleep) needs core code hacking for full support, otherwise the assembler throws an error regarding missing deep_sleep.h

NB: Deep sleep is currently ONLY supported on BK7321N. Other Beken variants are unsupported

Currently deep_sleep: is blocked from being defined in a Beken config

Please bring BK7321N deep sleep into the main code and in the meantime relax the inclusion restriction

Use cases

Support of battery operated Beken devices

Visual examples

No response

Anything else?

https://github.com/szupi-ipuzs/esphome-external-lt-deepsleep
https://github.com/libretiny-eu/libretiny-esphome/pull/11