arm: vt8500: Update arch-vt8500 to devicetree support.

Merged existing board files to a single dt-capable file.
Converted irq and timer code to devicetree.
Removed existing device files that are no longer required with
devicetree support.
All existing platform devices are converted to devicetree nodes
except PWM.

Removed restart.c and moved code into vt8500.c to remove
duplicate PMC code.

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