spi/pl022: Add loopback support for the SPI on 5500

Extend the vendor data with a loopback field, and add new
amba-pl022 vendor data for the DB5500 pl023, as the pl023
on db8500 and db5500 vary.

Signed-off-by: Prajadevi H <prajadevi.h@stericsson.com>
Signed-off-by: Philippe Langlais <philippe.langlais@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>