Hack in support for other boards/microcontrollers, add GpioDriver

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

firmware/Bsp/Drivers/LowPower.cpp

@@ -23,7 +23,7 @@
 #include "Bsp/Drivers/LowPower.h"
 #include "Bsp/macros.h"
 
-#include "stm32l0xx.h"
+#include "Mcu.h"
 
 uint32_t wakeups = 0;
 
@@ -56,7 +56,12 @@ ReturnCode LowPower::disable_debug()
     CLR(DBGMCU->CR, DBGMCU_CR_DBG_SLEEP);
     CLR(DBGMCU->CR, DBGMCU_CR_DBG_STANDBY);
 
+#if defined(STM32L0XX)
     CLR(RCC->APB2SMENR, RCC_APB2SMENR_DBGSMEN);
+#elif defined(STM32L4XX)
+#else
+    #error "Unsupported device type"
+#endif
 
     return ReturnCode::OK;
 }
@@ -70,12 +75,24 @@ ReturnCode LowPower::sleep()
 
 ReturnCode LowPower::stop()
 {
+#if defined(STM32L0XX)
     SET(PWR->CR, PWR_CR_CWUF); // clear wakeup flag
     while(PWR->CSR & PWR_CSR_WUF) {};
 
     CLR(PWR->CR, PWR_CR_PDDS); // Enter stop mode when the CPU enters deepsleep
     CLR(RCC->CFGR, RCC_CFGR_STOPWUCK); // MSI oscillator is wake-up from stop clock
     SET(SCB->SCR, SCB_SCR_SLEEPDEEP_Msk); // low-power mode = stop mode
+#elif defined(STM32L4XX)
+    SET(PWR->SCR, PWR_SCR_CWUF1); // clear wakeup flag
+
+    while(PWR->SR1 & PWR_SR1_WUF1) {};
+    SET_TO(PWR->CR1, PWR_CR1_LPMS, 1 << PWR_CR1_LPMS_Pos); // Enter stop mode 1 when the CPU enters deepsleep
+    CLR(RCC->CFGR, RCC_CFGR_STOPWUCK); // MSI oscillator is wake-up from stop clock
+    SET(SCB->SCR, SCB_SCR_SLEEPDEEP_Msk); // low-power mode = stop mode
+
+#else
+    #error "Unsupported device type"
+#endif
     __WFI(); // enter low-power mode (Wake from interrupt)
 
     wakeups++;