add 'stm32l052dap52' (STM32L052K8 MCU) board target

[majbthrd]

This adds the ST STM32L052 since I encountered a target with said MCU and didn't find an existing board type in TinyUSB.

I tried to follow the newer TinyUSB convention of "boards" sub-directory for a given "family" (stm32l0). There is an existing "stm32l0538disco" board using the older convention that I left untouched since I don't know the reasons behind it still being in the main bsp directory.

I set the board name to "stm32l052dap52". The reason for the naming suffix is that the target that I encountered is the Olimex LoRa-STM32WL-DevKIT, which uses a STM32L052K8 as a CMSIS-DAP adapter for the board's main target, which is a STM32WLE5-series (no USB capability). 'dap52' using the VID:PID 15ba:0044 appears to be Olimex's name of their (slightly buggy) fork of dap42

Olimex did not do the user any favors. Although there is talk in their github repository about a bootloader, that appears to just be leftover verbiage from the dap42 project. There is a SB1 in the schematic labelled "Bootloader", but it doesn't invoke anything. The only practical way to reprogram the STM32L052K8 is via the SWD pins on CON1 (1x10 IDC header).