staging: Replace all spi->chip_select and spi->cs_gpiod references with function call

Supporting multi-cs in spi drivers would require the chip_select & cs_gpiod
members of struct spi_device to be an array. But changing the type of these
members to array would break the spi driver functionality. To make the
transition smoother introduced four new APIs to get/set the
spi->chip_select & spi->cs_gpiod and replaced all spi->chip_select and
spi->cs_gpiod references with get or set API calls.
While adding multi-cs support in further patches the chip_select & cs_gpiod
members of the spi_device structure would be converted to arrays & the
"idx" parameter of the APIs would be used as array index i.e.,
spi->chip_select[idx] & spi->cs_gpiod[idx] respectively.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/20230310173217.3429788-6-amit.kumar-mahapatra@amd.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/staging/fbtft/fbtft-core.c

@@ -840,7 +840,7 @@ int fbtft_register_framebuffer(struct fb_info *fb_info)
 		sprintf(text1, ", %zu KiB buffer memory", par->txbuf.len >> 10);
 	if (spi)
 		sprintf(text2, ", spi%d.%d at %d MHz", spi->master->bus_num,
-			spi->chip_select, spi->max_speed_hz / 1000000);
+			spi_get_chipselect(spi, 0), spi->max_speed_hz / 1000000);
 	dev_info(fb_info->dev,
 		 "%s frame buffer, %dx%d, %d KiB video memory%s, fps=%lu%s\n",
 		 fb_info->fix.id, fb_info->var.xres, fb_info->var.yres,

drivers/staging/greybus/spilib.c

@@ -237,7 +237,7 @@ static struct gb_operation *gb_spi_operation_create(struct gb_spilib *spi,
 	request = operation->request->payload;
 	request->count = cpu_to_le16(count);
 	request->mode = dev->mode;
-	request->chip_select = dev->chip_select;
+	request->chip_select = spi_get_chipselect(dev, 0);
 
 	gb_xfer = &request->transfers[0];
 	tx_data = gb_xfer + count;	/* place tx data after last gb_xfer */