make sure splash start and end markers have correct position

Compiler can change position of start/end splash markers or even optimize-out
them completely, because they are not used in the fw. 
Make them part of the splash data block, so their possition is always correct.
util/xbm2lbm was changed together with other c "images" to make it consitent.

src/open9x.cpp

@@ -22,9 +22,10 @@
 #include "open9x.h"
 
 #ifdef SPLASH
-const pm_uchar spsMarker[] PROGMEM = { "SPS" };
+const pm_uchar splashdata[] PROGMEM = { 'S','P','S',0,
 #include "s9xsplash.lbm"
-const pm_uchar speMarker[] PROGMEM = { "SPE" };
+	'S','P','E',0};
+const pm_uchar * s9xsplash = splashdata+4;
 #endif
 
 #include "menus.h"