Kernel: Add a beep() syscall that beeps the PC speaker.

Hook this up in Terminal so that the '\a' character generates a beep.
Finally emit an '\a' character in the shell line editing code when
backspacing at the start of the line.

Kernel/Makefile

@@ -49,6 +49,7 @@ KERNEL_OBJS = \
        Net/Routing.o \
        Net/NetworkTask.o \
        ProcessTracer.o \
+       Devices/PCSpeaker.o \
        File.o
 
 VFS_OBJS = \