The Armada SoC family implementation of this SPI hardware module has
extended the configuration register to allow for a wider range of SPI
clock rates. Specifically the Serial Baud Rate Pre-selection bits in the
SPI Interface Configuration Register now also use bits 6 and 7 as well.

Modify the baud rate calculation to handle these differences for the
Armada case. Potentially a baud rate can be setup using a number of
different pre-scalar and scalar combinations. This code tries all
possible pre-scalar divisors (8 in total) to try and find the most
accurate set.

This change introduces (and documents) a new device tree compatible
device name "armada-370-spi" to support this.
Signed-off-by: NGreg Ungerer <gerg@uclinux.org>
Tested-by: NEzequiel Garcia <ezequiel.garcia@free-electrons.com>
Reviewed-by: NEzequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: NMark Brown <broonie@kernel.org>