Guard RCC registers access with critical section (#854)

* Core: critical section macros. FuriHal: guard rcc registers access with critical section, fix condition race.
* FuriHal: update documentation.

Co-authored-by: SG <who.just.the.doctor@gmail.com>

core/furi/common_defines.h

@@ -70,4 +70,14 @@
 #define REVERSE_BYTES_U32(x)                                                        \
     ((((x)&0x000000FF) << 24) | (((x)&0x0000FF00) << 8) | (((x)&0x00FF0000) >> 8) | \
      (((x)&0xFF000000) >> 24))
+#endif
+
+#ifndef FURI_CRITICAL_ENTER
+#define FURI_CRITICAL_ENTER()               \
+    uint32_t primask_bit = __get_PRIMASK(); \
+    __disable_irq()
+#endif
+
+#ifndef FURI_CRITICAL_EXIT
+#define FURI_CRITICAL_EXIT() __set_PRIMASK(primask_bit)
 #endif