ARM: realview: add flash devices to the PB1176 DTS

This adds the flash memories and ROM to the PB1175 DTS file.
The secure flash is marked as "disabled" by default so as to
protect the user from overwriting the boot monitor.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>