ARM: ux500: Rename MSP board file to something more meaningful

The 'msp' board file does more than just register MSP devices. It
also registers some other components necessary to get audio working
on ux500 based platforms; such as the PCM and Machine Drivers. For
that reason we're changing the filename to be more encompassing -
'audio'.

Acked-by: Ola Lilja <ola.o.lilja@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>