ARM: PL08x: remove circular buffer support

The driver already won't initialize a channel with a circular buffer;
the check in pl08x_prep_channel_resources() sees to that.  Remove
circular buffer support for the time being.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>