packagegroup-base: use amixer instead of alsamixer

packagegroup-base: use amixer instead of alsamixer

Including alsamixer, which is an ncurses based interactive program,
does not seem to make sense as a base package in embedded systems,
replace it by the command line mixer utility amixer instead; it is
scriptable and has no ncurses dependencies.

Signed-off-by: Diego Santa Cruz <Diego.SantaCruz@spinetix.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>