ARM: versatile: move flash registration to the device tree

This moves the boardfile definition of the flash memory in the
Versatile board into the device tree. The flash was already
defined with the property "arm,versatile-flash" which was
not handled by the kernel: instead define it as compatible
also with "cfi-flash" so it detects properly, and delete the
corresponding boardfile code so we get a smooth transition.

The old compatible string "arm,versatile-flash" is reused to
indicate to the MTD physmap subsystem that this flash requires
special VPP handling. (See separate patch.)

Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>