ARM: vt8500: Convert arch-vt8500 to multiplatform

This patch almosts completes the conversion to ARCH_MULTI_V5
for arch-vt8500.

Both single platform and multiplatform configurations are supported
until earlyprintk support is available for multiplatform.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
Acked-by: Arnd Bergmann <arnd@arndb.de>