spi: s3c64xx: allow full FIFO masks

spi: s3c64xx: allow full FIFO masks

The driver is wrong because is using partial register field masks for the
SPI_STATUS.{RX, TX}_FIFO_LVL register fields.

We see s3c64xx_spi_port_config.fifo_lvl_mask with different values for
different instances of the same IP. Take s5pv210_spi_port_config for
example, it defines:
	.fifo_lvl_mask  = { 0x1ff, 0x7F },

fifo_lvl_mask is used to determine the FIFO depth of the instance of the
IP. In this case, the integrator uses a 256 bytes FIFO for the first SPI
instance of the IP, and a 64 bytes FIFO for the second instance. While
the first mask reflects the SPI_STATUS.{RX, TX}_FIFO_LVL register
fields, the second one is two bits short. Using partial field masks is
misleading and can hide problems of the driver's logic.

Allow platforms to specify the full FIFO mask, regardless of the FIFO
depth.

Introduce {rx, tx}_fifomask to represent the SPI_STATUS.{RX, TX}_FIFO_LVL
register fields. It's a shifted mask defining the field's length and
position. We'll be able to deprecate the use of @rx_lvl_offset, as the
shift value can be determined from the mask. The existing compatibles
shall start using {rx, tx}_fifomask so that they use the full field mask
and to avoid shifting the mask to position, and then shifting it back to
zero in the {TX, RX}_FIFO_LVL macros.

@rx_lvl_offset will be deprecated in a further patch, after we have the
infrastructure to deprecate @fifo_lvl_mask as well.

No functional change intended.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://msgid.link/r/20240216070555.2483977-4-tudor.ambarus@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>