mfd: Add Samsung Exynos Low Power Audio Subsystem driver

This patch adds common driver for the Top block of the Samsung Exynos
SoC Low Power Audio Subsystem.  This is a minimal driver which prepares
resources for IP blocks like I2S, audio DMA and UART and exposes
a regmap for the Top block registers.  Also system power ops are added
to ensure the Audio Subsystem is operational after system suspend/resume
cycle.

Signed-off-by: Inha Song <ideal.song@samsung.com>
Signed-off-by: Beomho Seo <beomho.seo@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>