mfd: davinci_voicecodec: Tidyup header difinitions

mach/hardware.h is needed on C source code side, not header.
And struct davinci_vc is duplicated definition.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>