mtd: drop Integrator flash map Kconfig

The integrator flash has been deleted, even from the Makefile.
Drop the Kconfig entry as well.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>