at91: Refactor Stamp9G20 and PControl G20 board file

As PControl G20 is a carrier board for the Stamp9G20 SoM, some code can
be shared. Therefore board-stamp9g20.c is refactored to allow reusing the
SoM initialization and board-pcontrol-g20.c is modified to use it.

Signed-off-by: Christian Glindkamp <christian.glindkamp@taskit.de>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
diff --git a/arch/arm/mach-at91/Makefile b/arch/arm/mach-at91/Makefile
index 62d686f..d13add7 100644
--- a/arch/arm/mach-at91/Makefile
+++ b/arch/arm/mach-at91/Makefile
@@ -65,7 +65,7 @@
 obj-$(CONFIG_MACH_CPU9G20)	+= board-cpu9krea.o
 obj-$(CONFIG_MACH_STAMP9G20)	+= board-stamp9g20.o
 obj-$(CONFIG_MACH_PORTUXG20)	+= board-stamp9g20.o
-obj-$(CONFIG_MACH_PCONTROL_G20)	+= board-pcontrol-g20.o
+obj-$(CONFIG_MACH_PCONTROL_G20)	+= board-pcontrol-g20.o board-stamp9g20.o
 
 # AT91SAM9260/AT91SAM9G20 board-specific support
 obj-$(CONFIG_MACH_SNAPPER_9260)	+= board-snapper9260.o