Add device-width property to pflash_cfi01

The width of the devices that make up the flash interface
is required to mask certain commands, in particular the
write length for buffered writes.  This length will be presented
to each device on the interface by the program writing the flash,
and the flash emulation code needs to be able to determine
the length of the write as recieved by each flash device.
The device-width defaults to the bank width which should
maintain existing behavior for platforms that don't need
this change.
This change is required to support buffered writes on the
vexpress platform that has a 32 bit flash interface with 2
16 bit devices on it.

Signed-off-by: Roy Franz <roy.franz@linaro.org>
Message-id: 1386279359-32286-3-git-send-email-roy.franz@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>