Hack in support for other boards/microcontrollers, add GpioDriver

There's definitely plenty of cleanup work to be done (see:
"ifdefs").

firmware/Bsp/Drivers/LptimPwm.cpp

@@ -34,9 +34,15 @@ LptimPwm::LptimPwm(LPTIM_TypeDef *lptim)
 void LptimPwm::init_lptim()
 {
     /* Enable LPTIM in APB1 */
+#if defined(STM32L0XX)
     SET(RCC->APB1ENR,
         RCC_APB1ENR_LPTIM1EN);
-
+#elif defined(STM32L4XX)
+    SET(RCC->APB1ENR1,
+        RCC_APB1ENR1_LPTIM1EN);
+#else
+#error "Unsupported family"
+#endif
     // Enable low-speed internal
     RCC->CSR |= RCC_CSR_LSION;
     while (!(RCC->CSR & RCC_CSR_LSIRDY)) {};
@@ -90,21 +96,6 @@ ReturnCode LptimPwm::init()
 {
     init_lptim();
 
-    /* Enable GPIO port A */
-    SET(RCC->IOPENR, RCC_IOPENR_IOPAEN);
-
-    /* Assign LPTIM1_OUT to PA7 */
-    SET_TO(GPIOA->AFR[0],
-           GPIO_AFRL_AFRL7,
-           1u << GPIO_AFRL_AFRL7_Pos);
-
-    SET_TO(GPIOA->MODER,
-           GPIO_MODER_MODE7,
-           2u << GPIO_MODER_MODE7_Pos);
-
-    CLR(GPIOA->OTYPER, GPIO_OTYPER_OT_7);
-    CLR(GPIOA->PUPDR, GPIO_PUPDR_PUPD7);
-
     return ReturnCode::OK;
 }