Kernel/LibC/Userspace: Add SYS_POWEROFF + cli tool

You can now shutdown/reboot banan-os with the poweroff cli tool.

Reboot doesn't seem to work on qemu.

libc/include/sys/banan-os.h

@@ -11,8 +11,8 @@ __BEGIN_DECLS
 #define TTY_FLAG_ENABLE_OUTPUT	1
 #define TTY_FLAG_ENABLE_INPUT	2
 
-#define POWER_SHUTDOWN 0
-#define POWER_REBOOT 1
+#define POWEROFF_SHUTDOWN 0
+#define POWEROFF_REBOOT 1
 
 /*
 fildes:		refers to valid tty device
@@ -22,6 +22,7 @@ flags:		bitwise or of TTY_FLAG_* definitions
 return value: 0 on success, -1 on failure and errno set to the error
 */
 int tty_ctrl(int fildes, int command, int flags);
+int poweroff(int command);
 
 __END_DECLS
 

libc/include/sys/syscall.h

@@ -54,6 +54,7 @@ __BEGIN_DECLS
 #define SYS_MMAP 51
 #define SYS_MUNMAP 52
 #define SYS_TTY_CTRL 53
+#define SYS_POWEROFF 54
 
 __END_DECLS