ENGR00230920-1 HDMI AUDIO: add support for HDMI audio module build
HDMI driver can be divided into 3 parts: machine driver, platform
driver, codec driver.To support HDMI AUDIO loadable module build, HDMI
machine driver should be built as loadable.
In this patch, adjust HDMI audio driver's struct: move HDMI audio platform
driver to snd-soc-imx-objs(snd-soc-imx-objs would always be
build-in).In this case, user need only build HDMI AUDIO machine driver
as loadable.