ASoC: Rename ep93xx soc directory to cirrus

This patch is to rename the directory "ep93xx" in "cirrus".
Name more accurately reflects the manufacturer and allows to add
drivers not only for architecture ep93xx in this directory.
Patch not contain any functional changes.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>