Add support for the Linux SPI subsystem (spidev)

See http://www.kernel.org/doc/Documentation/spi/spidev for an introduction.

Usage is as follows:

  flashrom -p linux_spi:dev=/dev/spidevX.Y

where X is the bus number, and Y device. It accepts an optional parameter
'speed' which allows to set the SPI clock speed in kHz.

Tested on an Atmel AVR32AP7000 board (NGW100 Network Gateway Kit), see
below, which was used to program a ThinkPad X60, but it should work on every
other Linux system, too.
  
  http://www.atmel.com/dyn/products/tools_card.asp?tool_id=4102)

Corresponding to flashrom svn r1427.

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Acked-by: Uwe Hermann <uwe@hermann-uwe.de>
diff --git a/Makefile b/Makefile
index 9ad9d95..6407e6b 100644
--- a/Makefile
+++ b/Makefile
@@ -313,6 +313,10 @@
 # Always enable Bus Pirate SPI for now.
 CONFIG_BUSPIRATE_SPI ?= yes
 
+# Disable Linux spidev interface support for now, until we check for a Linux
+# device (not host, as DOS binaries for example are built on a Linux host).
+CONFIG_LINUX_SPI ?= no
+
 # Disable Dediprog SF100 until support is complete and tested.
 CONFIG_DEDIPROG ?= no
 
@@ -449,6 +453,11 @@
 NEED_SERIAL := yes
 endif
 
+ifeq ($(CONFIG_LINUX_SPI), yes)
+FEATURE_CFLAGS += -D'CONFIG_LINUX_SPI=1'
+PROGRAMMER_OBJS += linux_spi.o
+endif
+
 ifeq ($(CONFIG_DEDIPROG), yes)
 FEATURE_CFLAGS += -D'CONFIG_DEDIPROG=1'
 FEATURE_LIBS += -lusb