Use defines for register CPU2X instead of hex value

Prepare PolledTimeout for dynamic CPU frequency - would fail to compile if F_CPU is not defined, helps as marker that something needs to be done.

Author: dok-net

Diff for: cores/esp8266/PolledTimeout.h

@@ -76,7 +76,7 @@ struct TimeSourceCycles
 
   using timeType = decltype(ESP.getCycleCount());
   static timeType time() {return ESP.getCycleCount();}
-  static constexpr timeType ticksPerSecond    = F_CPU;     // 80'000'000 or 160'000'000 Hz
+  static constexpr timeType ticksPerSecond    = ESP.getCpuFreqMHz() * 1000000UL;     // 80'000'000 or 160'000'000 Hz
   static constexpr timeType ticksPerSecondMax = 160000000; // 160MHz
 };
 

Diff for: cores/esp8266/core_esp8266_main.cpp

@@ -84,9 +84,11 @@ void initVariant() {
 extern "C" void __preloop_update_frequency() {
 #if defined(F_CPU) && (F_CPU == 160000000L)
     ets_update_cpu_frequency(160);
-    REG_SET_BIT(0x3ff00014, BIT(0));
+    CPU2X |= 1;
 #elif !defined(F_CPU)
-    if (system_get_cpu_freq() == 160) REG_SET_BIT(0x3ff00014, BIT(0));
+    if (system_get_cpu_freq() == 160) {
+        CPU2X |= 1;
+    }
 #endif
 }