[nrf noup] Clean Kconfig.defaults to support "Thread and Wi-Fi" builds

[Damian-Nordic]

1. Group Kconfig options into categories to make it easier to see discrepancies between Thread and Wi-Fi and help choose the right value when both transports are enabled.

   That is, prefer:

   config A
     default X if CHIP_WIFI
     default Y if NET_L2_OPENTHREAD
   

   over:

   if CHIP_WIFI
   config A
     default X
   endif
   
   if NET_L2_OPENTHREAD
   config A
     default Y
   endif
   

2. Remove redundant defaults that are already selected in other Kconfig files.

3. Enable SHA1 for Wi-Fi

[LuDuda]

This is fantastic! Thank you so much!

Just a question: Are we able to easily check (other than in manual way) if some of the configuration in Kconfig.defaults are not necessary anymore? For example with introduction of SHELL_MINIMAL i do see now, that i could have removed KERNEL_SHELL config. I bet, some other configs are not needed anymore as well.

[Damian-Nordic]

This is fantastic! Thank you so much!

Just a question: Are we able to easily check (other than in manual way) if some of the configuration in Kconfig.defaults are not necessary anymore? For example with introduction of SHELL_MINIMAL i do see now, that i could have removed KERNEL_SHELL config. I bet, some other configs are not needed anymore as well.

I don't know, we would need to write a script that removes random configs and checks if .config hasn't changed, but I'm not aware of such a tool.