stm32/mboot: Remove custom HAL_RCC_GetHCLKFreq and use HAL provided one.

So that a board can access other HAL_RCC functions if it needs them (this
was not possible previously by just adding hal_rcc.c to the src list for a
board because it would clash with the custom HAL_RCC_GetHCLKFreq function).

Signed-off-by: Damien George <damien@micropython.org>

ports/stm32/mboot/Makefile

@@ -161,6 +161,7 @@ SRC_HAL += $(addprefix $(HAL_DIR)/Src/stm32$(MCU_SERIES)xx_,\
 	hal_flash_ex.c \
 	hal_pcd.c \
 	hal_pcd_ex.c \
+	hal_rcc.c \
 	ll_usb.c \
 	)
 

ports/stm32/mboot/main.c

@@ -326,11 +326,6 @@ void SystemClock_Config(void) {
 
 #endif
 
-// Needed by HAL_PCD_IRQHandler
-uint32_t HAL_RCC_GetHCLKFreq(void) {
-    return SystemCoreClock;
-}
-
 /******************************************************************************/
 // GPIO