ARM: dts: Remove mau_pd node for exynos5420

MAU powerdomain provides clocks for Audio sub-system block.
This block comprises of the I2S audio controller, audio DMA
blocks and Audio sub-system clock registers.

Right now, there is no way to hook up power-domains with
clock providers.  During late boot when this power-domain
gets disabled, we get following external abort.

Unhandled fault: imprecise external abort (0x1406) at 0x00000000
Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000007

Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>