spi: Add Meson SPICC driver

The SPICC hardware block on the Amlogic SoCs is Communication oriented and
can do Full-Duplex 8- to 32-bit width SPI transfers up to 30MHz.

The current driver only supportd the PIO transfer mode since the DMA seems
broken on available hardware.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>