spi: aspeed: Add support for the AST2400 SPI controller

Extend the driver for the AST2400 SPI Flash Controller (SPI). This
controller has a slightly different interface which requires
adaptation of the 4B handling. Summary of features :

   . host Firmware
   . 1 chip select pin (CE0)
   . slightly different register set, between AST2500 and the legacy
     controller
   . no segment registers
   . single, dual mode.

Reviewed-by: Joel Stanley <joel@jms.id.au>
Tested-by: Joel Stanley <joel@jms.id.au>
Tested-by: Tao Ren <rentao.bupt@gmail.com>
Tested-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Link: https://lore.kernel.org/r/20220509175616.1089346-8-clg@kaod.org


Signed-off-by: Mark Brown <broonie@kernel.org>