i2c: designware: Add SMBUS quick command support

The SMBUS emulation code turns an SMBUS quick command into a zero-
length read. This controller can't do zero length accesses, but it
can do quick commands, so reverse the emulation. The alternative
would be to properly implement the SMBUS support but that is a lot
more work, and unnecessary just to get i2cdetect working.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>