spi: meson-spicc: add support for Amlogic G12A

Add support for the SPICC controllers on the Amlogic G12A SoCs family.

The G12A SPICC controllers inherit from the AXG enhanced registers but
takes an external pclk for the baud rate generator and can achieve up to
166MHz SCLK.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20200312133131.26430-10-narmstrong@baylibre.com


Signed-off-by: Mark Brown <broonie@kernel.org>