ARM: davinci: Set proper SPI prescale limit value

SPI Davinci driver has been updated to allow SOCs to specify their minimum
prescale value. Update the various SOCs board files that use this driver with
their proper prescaler limit.

Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>