tests: add a m25p80 test

tests: add a m25p80 test

This test uses the palmetto platform and the Aspeed SPI controller to
test the m25p80 flash module device model. The flash model is defined
by the platform (n25q256a) and it would be nice to find way to control
it, using a property probably.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1475787271-28794-1-git-send-email-clg@kaod.org
Brainstormed-with: Greg Kurz <groug@kaod.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>