spidev_test utility

This is a simple utility used to test SPI functionality.  It could stand
growing options to support using other test data patterns; this initial
version only issues full duplex transfers, which rules out 3WIRE or
Microwire links.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>