Audio subsystem clocks are located in separate block. On Exynos 5420 if
clock for this block (from main clock domain) 'mau_epll' is gated then
any read or write to audss registers will block.

This kind of boot hang was observed on Arndale Octa and Peach Pi/Pit
after introducing runtime PM to pl330 DMA driver. After that commit the
'mau_epll' was gated, because the "amba" clock was disabled and there
were no more users of mau_epll.

The system hang on one of steps:
1. Disabling unused clocks from audss block.
2. During audss GPIO setup (just before probing i2s0 because
   samsung_pinmux_setup() tried to access memory from audss block which was
   gated.

Add a workaround for this by enabling the 'mau_epll' clock in probe.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Acked-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Michael Turquette <mturquette@linaro.org>