Picking a HAL for stm32l151

[hdhoang]

Must haves:

• USB support, with usb-device+stm32-usbd as keyberon requests
• GPIO, USART support (all do)
• cortex-m >= 0.7

Nice to haves:

• More knowledgable support
• Reasonably easy to update PAC dep
• Explicit resource loans, eg GPIO split with &mut RCC. This will help keeping flow straight for a newb like me

Bases:

• ah-/stm32l151-hal
• stm32-hal2
• stm32l1xx-hal
• stm32l0xx-hal, f1, f4 as copy source

[hdhoang]

now embassy supports this chip too https://github.com/embassy-rs/embassy/pull/399

[hdhoang]

l1xx-hal has WIP at https://github.com/stm32-rs/stm32l1xx-hal/pull/14/files 🎉