Fix on PS and factory reset

First PS was erased when 8 chars was reached. Not all stations use 8 char PS. Changed the routine. First 8 RDS decoding runs after a tune command PS is written dirty, to have it DX-fast. After that, PS will be written when offset reaches 0.

Also added factory reset. Hold BW+STEP pressed during boot.

src/TEF6686.h

@@ -268,5 +268,6 @@ class TEF6686 {
     uint16_t rdsDprevious;
     bool correctpi;
     bool rtABold;
-    wchar_t PStext[9] = L"";           
+    wchar_t PStext[9] = L"";
+    byte ps_counter;
 };