Set proper device-width for vexpress flash

Set proper device-width for vexpress flash

Create vexpress specific pflash registration
function which properly configures the device-width
of 16 bits (2 bytes) for the NOR flash on the
vexpress platform.  This change is required for
buffered flash writes to work properly.

Signed-off-by: Roy Franz <roy.franz@linaro.org>
Message-id: 1386279359-32286-5-git-send-email-roy.franz@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>