avr32: Rename at32ap.c -> pdc.c

The only thing left in at32ap.c is some PDC stuff. Rename the file to
reflect what it actually does.
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

arch/avr32/mach-at32ap/Makefile

-obj-y				+= at32ap.o clock.o intc.o extint.o pio.o hsmc.o
+obj-y				+= pdc.o clock.o intc.o extint.o pio.o hsmc.o
 obj-$(CONFIG_CPU_AT32AP700X)	+= at32ap700x.o pm-at32ap700x.o
 obj-$(CONFIG_CPU_FREQ_AT32AP)	+= cpufreq.o