spi: spi-rspi: Add support to deassert/assert reset line

spi: spi-rspi: Add support to deassert/assert reset line

On RZ/G2L SoC we need to explicitly deassert the reset line
for the device to work, use this opportunity to deassert/assert
reset line in spi-rspi driver.

This patch adds support to read the "resets" property (if available)
from DT and perform deassert/assert when required.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211118031041.2312-3-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>