kernel: add e9 device for debugging

kernel-src/include/kernel/devfs.h

@@ -12,6 +12,7 @@
 #define DEV_MAJOR_FB 5
 #define DEV_MAJOR_KEYBOARD 6
 #define DEV_MAJOR_BLOCK 7
+#define DEV_MAJOR_E9 8
 
 typedef struct {
 	int (*open)(int minor, int flags);

kernel-src/include/x86-64/arch/e9.h

@@ -3,5 +3,6 @@
 
 void arch_e9_putc(char);
 void arch_e9_puts(char *);
+void arch_e9_initdev();
 
 #endif