mach-ux500: rename PRCMU driver per SoC

This renames the prcmu.c file to prcmu-db8500.c so as to indicate
that it is for this one SoC.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

arch/arm/mach-ux500/Makefile

@@ -5,7 +5,7 @@
 obj-y				:= clock.o cpu.o devices.o devices-common.o \
 				   id.o usb.o
 obj-$(CONFIG_UX500_SOC_DB5500)	+= cpu-db5500.o dma-db5500.o
-obj-$(CONFIG_UX500_SOC_DB8500)	+= cpu-db8500.o devices-db8500.o prcmu.o
+obj-$(CONFIG_UX500_SOC_DB8500)	+= cpu-db8500.o devices-db8500.o prcmu-db8500.o
 obj-$(CONFIG_MACH_U8500)	+= board-mop500.o board-mop500-sdi.o \
 				board-mop500-regulators.o \
 				board-mop500-uib.o board-mop500-stuib.o \