ARM: plat-mxc: audmux-v1: Remove unneeded ifdef's

As we are able to build a single kernel that can run on mx21 and mx27,
there is no need for the ifdef's anymore inside audmux-v1.c.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>