dts: vt8500: Fix invalid/missing cpu nodes for soc files.

vt8500, wm8650 and wm8850 have no cpu node specified.
wm8505 has a cpu node which contains an invalid compatible string, and
is missing the other required properties.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>
dts: vt8500: Add devicetree support for WM8750 SoC and APC8750 board

This patch adds support for the WonderMedia WM8750 SoC and the VIA
APC8750 board.

Signed-off-by: Tony Prisk <linux@prisktech.co.nz>