ARM: 6904/1: MTD: Add integrator-flash feature to physmap

In the process of moving platforms away from integrator-flash
(aka armflash), add to physmap the few features that make
armflash unique:

- optionnal probing for the AFS partition type
- init() and exit() methods, used by Integrator to control
  write access to the various onboard programmable components

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>