Keyboard scancode set switching and set 1 support (#546)

This improvement allows the use of set 1 of keyboard scancodes, as well as the possibility of changing from one to another from the OS. Both core ao486 and new cores based on set 1 will benefit from this feature.

Thank you @naeloob for your cooperation and support in developing this feature.

main.cpp

@@ -34,6 +34,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "osd.h"
 
 const char *version = "$VER:" VDATE;
+uint8_t ps2_kbd_scan_set = 2;
 
 int main(int argc, char *argv[])
 {