clk: davinci: psc-dm365: fix few clocks

Fix parent of EMAC and voice codec PSC clocks. Documentation is clear
on EMAC clock parent, but its not fully clear on parent of voice codec
clock. The implementation chosen is matches arch/arm/mach-davinci/dm365.c.
Add a comment explaining this for posterity.

There is only one power domain on DM365. Fix the power domain of voice
codec and vpss dac modules.

While at it, add a comment explaining how the parent of vpss dac clock was
derived. Note that this patch does not touch the parent of vpss dac clock.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Reviewed-by: David Lechner <david@lechnology.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20180525181150.17873-6-david@lechnology.com