spi: orion: Fix extended baud rates for each Armada SoCs

The commit df59fa7f "spi: orion: support armada extended baud
rates" made the assumptions that all the Armada SoCs supported the
same maximum frequency. However, according the hardware datasheet, the
maximum frequency supported by the Armada 370 SoC is tclk/4, for the
Armada XP, Armada 38x and Armada 39x SoCs the limitation is 50MHz and
for the Armada 375 it is tclk/15.

This patch introduces new compatible strings to handle all these
case. In order to be future proof a compatible was created for each
SoC even if currently some SoCs seem using the same IP.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Mark Brown <broonie@kernel.org>