ASoC: Shrink code size for WM8962 register defaults table

Dramatically reduce the code size for the WM8962 register defaults table
by switching to explicitly initialise only defined registers, relying on
static defaulting to zero for the overwelming bulk of the register map.

Similar treatement for the register access table will come later and will
produce a similarly dramatic code size shrink.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>