spi/amba-pl022: work in polling or interrupt mode if pl022_dma_probe fails

If pl022_dma_probe fails, we can try to transfer data in polling or interrupt
mode. Also, set platform_info->enable_dma to 0, so that no other code tries to
use dma.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>