mfd: exynos-lpass: Enable UART module support

This patch enables proper interrupts routing between UART module
in Exynos Audio SubSystem and the rest of the SoC. This routing is
completely transparent for UART device and CPU/GIC. UART driver requests
interrupts from the respective controller and enables/masks/handles it
by itself via standard methods.

There are boards (for example TM2), which use UART module in Exynos Audio
SubStem for communication with BlueTooth chip.

Signed-off-by: Beomho Seo <beomho.seo@samsung.com>
[mszyprow: rephrased commit message, added UART reset]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>