add memory mapped registers for keyboard status and data

tyvm.c

@@ -30,6 +30,12 @@
 #define FALSE 0
 
 
+/* memory mapped register tables */
+enum mmr {
+    MMR_KSR = 0xFE00,   // keyboard status
+    MMR_KDR = 0xFE02    // keyboard data
+}
+
 /* Initializing 10 registers of which:
 8 general purpose, 1 program counter, 1 conditional */
 enum registers {