spi: designware_spi: Add reset ctrl to driver

Add code to reset all reset signals as in SPI DT node. A reset property
is an optional feature, so only print out a warning and do not fail if a
reset property is not present.

If a reset property is discovered, then use it to deassert, thus
bringing the IP out of reset.

Release reset when _remove().

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
Acked-by: Marek Vasut <marex@denx.de>
Reviewed-by: Jagan Teki <jagan@openedev.com>