spi: tegra210-quad: Add support for hardware dummy cycles transfer

spi: tegra210-quad: Add support for hardware dummy cycles transfer

Tegra Quad SPI controller hardware supports sending dummy bytes based
on programmed dummy clock cycles after the actual transfer bytes.

This patch adds this support of hardware dummy bytes transfer and
skips transfer of dummy bytes from the software.

For dummy cycles more than Tegra Quad SPI hardware maximum dummy
cycles limit, driver transfers dummy bytes from the software.

Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Link: https://lore.kernel.org/r/1608585459-17250-7-git-send-email-skomatineni@nvidia.com
Signed-off-by: Mark Brown <broonie@kernel.org>