Add PIXIS FPGA support for MPC8641HPCN board.

Move the 8641HPCN's PIXIS code to the new directory
board/freescale/common/ as it will be shared by
future boards not in the same processor family.

Write a "pixis_reset" command that utilizes the FPGA
reset sequencer to support alternate soft-reset options
such as using the "alternate" flash bank, enabling
the watch dog, or choosing different CPU frequencies.

Add documentation for the pixis_reset to README.mpc8641hpcn.

Signed-off-by: Haiying Wang <haiying.wang@freescale.com>
Signed-off-by: Jon Loeliger <jdl@freescale.com>
diff --git a/board/mpc8641hpcn/Makefile b/board/mpc8641hpcn/Makefile
index 4b68c36..9625211 100644
--- a/board/mpc8641hpcn/Makefile
+++ b/board/mpc8641hpcn/Makefile
@@ -25,7 +25,9 @@
 
 LIB	= $(obj)lib$(BOARD).a
 
-COBJS	:= $(BOARD).o pixis.o sys_eeprom.o
+COBJS	:= $(BOARD).o sys_eeprom.o \
+		../freescale/common/pixis.o
+
 SOBJS	:= init.o
 
 SRCS	:= $(SOBJS:.o=.S) $(COBJS:.o=.c)