[ARM] 3818/1: iop3xx: introduce arch/arm/plat-iop for shared iop32x/iop33x code

Introduce the arch/arm/plat-iop directory, for code shared between the
iop32x and iop33x, and move the common memory map setup bits there.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>