integrated serial mouse drivers as a feature into the firmware architecture

* can be enabled by defining Makefile macro SERIAL_MOUSE_MICROSOFT_ENABLE or
   SERIAL_MOUSE_MOUSESYSTEMS_ENABLE.
 * Serial implementation can be chosen via SERIAL_MOUSE_USE_SOFT and
   SERIAL_MOUSE_USE_UART macros
 * UART configuration still has to be done in config.h: I added working clauses
   for both mouse protocols to ps2_usb's config.h

protocol.mk

@@ -23,5 +23,25 @@ ifdef PS2_USE_USART
 endif
 
 
+ifdef SERIAL_MOUSE_MICROSOFT_ENABLE
+    SRC += $(PROTOCOL_DIR)/serial_mouse_microsoft.c
+    OPT_DEFS += -DSERIAL_MOUSE_ENABLE -DSERIAL_MOUSE_MICROSOFT \
+                -DMOUSE_ENABLE
+endif
+
+ifdef SERIAL_MOUSE_MOUSESYSTEMS_ENABLE
+    SRC += $(PROTOCOL_DIR)/serial_mouse_mousesystems.c
+    OPT_DEFS += -DSERIAL_MOUSE_ENABLE -DSERIAL_MOUSE_MOUSESYSTEMS \
+                -DMOUSE_ENABLE
+endif
+
+ifdef SERIAL_MOUSE_USE_SOFT
+    SRC += $(PROTOCOL_DIR)/serial_soft.c
+endif
+
+ifdef SERIAL_MOUSE_USE_UART
+    SRC += $(PROTOCOL_DIR)/serial_uart.c
+endif
+
 # Search Path
 VPATH += $(TOP_DIR)/protocol