[FL-2480] Use SysTick as the main OS timer (#1140)

* Use SysTick as OS tick timer
* Use LPTIM2 as tickless idle timer
* Remove dummy LPTIM2 IRQ handler
* Clean up clock init code
* Rename os timer to idle timer
* Advance hal ticks along with FreeRTOS's
* Improve SysTick control during tickless idle
* Improve idle timer precision
* Correct SysTick IRQ priority
* Main, FuriHal: move system startup to separate thread
* Minor code cleanup

Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>

firmware/targets/f7/furi_hal/furi_hal_clock.h

@@ -14,3 +14,9 @@ void furi_hal_clock_switch_to_hsi();
 
 /** Switch to PLL clock */
 void furi_hal_clock_switch_to_pll();
+
+/** Stop SysTick counter without resetting */
+void furi_hal_clock_suspend_tick();
+
+/** Continue SysTick counter operation */
+void furi_hal_clock_resume_tick();