ASoC: remove unused ep93xx files

A couple of ep93xx board files were unused and got removed, so
the corresponding ASoC support can also be removed.

Cc: Mika Westerberg <mika.westerberg@iki.fi>
Cc: Ryan Mallon <rmallon@gmail.com>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>