While having some troubles replicating the no-sound-before-suspend issue, I added a few files just because it didn't take me long to write them...
I don't know how to send patches for review or how things are incorporated into the newark image, so I'm just sending the files here and hope that someone will review and pick them up (or possibly tell me how to properly send them).
The 90-tegra-rt5640.rules goes into /lib/udev/rules.d/
and the files in the alsa-mixer directory should be added to the /usr/share/pulseaudio/alsa-mixer directory on the image.
After a reboot (note: restarting pulseaudio is not enough), Sound settings will show one "Headphones" and one "Speaker" port, selecting one of them will cause sound to output through that port, and volume up/down to change volume of that port and not the other one.
There's no jack detection yet so after plugging in / unplugging, you would have to switch port manually in Sound Settings.
David Henningsson, Canonical Ltd.