[STM32] Removed exti.c from f1 and made global exti.c usable.

Because most changes are internal to a function in exti.c I am leaving
the macro checks in there, otherwise we would end up with a bunch of
code duplication if we used the dispatch system used otherwise
throughout the stm32 part of the library. I bet it could be split up
into more granular functions resulting in more generic code that we
could run through the dispatch system. But I am leaving that as an
excersize for later.

lib/stm32/f4/Makefile

@@ -34,7 +34,7 @@ CFLAGS		= -Os -g \
 # ARFLAGS	= rcsv
 ARFLAGS		= rcs
 
-OBJS		= adc.o can.o gpio.o exti2.o pwr.o rcc.o rtc.o crypto.o
+OBJS		= adc.o can.o gpio.o exti.o pwr.o rcc.o rtc.o crypto.o
 
 OBJS            += crc_common_all.o dac_common_all.o dma_common_f24.o \
                    gpio_common_all.o gpio_common_f234.o i2c_common_all.o \