spi: atmel-quadspi: Add cs_hold and cs_inactive setting support

spi: atmel-quadspi: Add cs_hold and cs_inactive setting support

spi-cs-inactive-delay-ns in dts is cs_inactive in spi core, and it maps
to DLYCS (Minimum Inactive QCS Delay) in QSPI Mode Register (QSPI_MR).

spi-cs-hold-delay-ns in dts is cs_hold in spi core, and it maps to
DLYBCT (Delay Between Consecutive Transfers) in QSPI_MR.  That one can
be set to other values than 0 only if the chip is not in Serial Memory
Mode (SMM), it must be written to '0' however when in SMM.

Tested on SAM9X60 based board with FPGA implementing custom SPI Memory
protocol.

Signed-off-by: Alexander Dahl <ada@thorsis.com>
Link: https://patch.msgid.link/20240918082744.379610-3-ada@thorsis.com
Signed-off-by: Mark Brown <broonie@kernel.org>