This ensures the fsl-alsa-plugins is installed per default by images
but allow it to be manually skipped, using BAD_RECOMMENDATIONS, if need.

This change has been based on a change done in meta-fsl-bsp-release,
3.5.7 dylan branch, which originally add this in the packagegroup-fsl
by Jun Zhu <R01007@freescale.com>.

The inclusion of this, inside imx-base.inc, is preferred as it is
common for all i.MX6 machines and not something specific for demos
thus should be installed by default.

Change-Id: I209d389b4e0a62b89b4fdede56627e0ec528df87
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>