Add UCMs for Google Asus Nexus 7 and Acer Iconia A500

[GitHub pull_request - reopened]

alsa-project/alsa-ucm-conf pull request #92 was reopened from digetx:

@perexg As was discussed previouly at https://www.spinics.net/lists/alsa-devel/msg126382.html I'm opening PR with the UCMs for  Nexus 7 and A500. Both these devices are supported by the mainline Linux kernel. 

You're right that Tegra ASoC driver doesn't set card's name properly. In particular I found that we need to set the card's `driver_name` to `tegra`, then UCM get a proper lookup path.

I rebased UCMs on top of the recent alsa-ucm-conf master and switched Nexus 7 UCM to use generic RT5640 UCM. Everything works great once the card name of the kernel driver is corrected. I'll send the kernel patches ASAP for review.

Nexus 7 alsa-info: https://alsa-project.org/db/?f=0a29f1dab39ec5b33e01215dee42dbfd1dbbf08e
A500 alsa-info: https://alsa-project.org/db/?f=bde4f7938a39b1d26904b414969fc811e726242f

The alsa-info is taken using the updated kernel ASoC driver.

Request URL   : https://github.com/alsa-project/alsa-ucm-conf/pull/92
Patch URL     : https://github.com/alsa-project/alsa-ucm-conf/pull/92.patch
Repository URL: https://github.com/alsa-project/alsa-ucm-conf