drivers: spi: gecko: eusart: Support LSB first and GPIO CS

Propagate bit ordering and type of CS pin to HAL layer. Previously,
the driver assumed MSB first and EUSART hardware CS control.

(cherry picked from commit 6b65d60)

Original-Signed-off-by: Aksel Skauge Mellbye <[email protected]>
GitOrigin-RevId: 6b65d60
Cr-Build-Id: 8727764308049365969
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8727764308049365969
Copybot-Job-Name: zephyr-main-copybot-downstream
Change-Id: I0542e91659011eaab4f362679113431ca0acb380
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/6116711
Commit-Queue: Fabio Baltieri <[email protected]>
Reviewed-by: Fabio Baltieri <[email protected]>
Tested-by: ChromeOS Prod (Robot) <[email protected]>

Author: Aksel Skauge Mellbye

drivers/spi/spi_gecko_eusart.c

@@ -82,11 +82,6 @@ static int spi_eusart_config(const struct device *dev, const struct spi_config *
 		return -ENOTSUP;
 	}
 
-	if (config->operation & SPI_TRANSFER_LSB) {
-		LOG_ERR("LSB first not supported");
-		return -ENOTSUP;
-	}
-
 	if (config->operation & SPI_OP_MODE_SLAVE) {
 		LOG_ERR("Slave mode not supported");
 		return -ENOTSUP;
@@ -133,6 +128,8 @@ static int spi_eusart_config(const struct device *dev, const struct spi_config *
 		eusartAdvancedSpiInit.csPolarity = eusartCsActiveLow;
 	}
 
+	eusartAdvancedSpiInit.msbFirst = !(config->operation & SPI_TRANSFER_LSB);
+	eusartAdvancedSpiInit.autoCsEnable = !spi_cs_is_gpio(config);
 	eusartInit.databits = eusartDataBits8;
 	eusartInit.advancedSettings = &eusartAdvancedSpiInit;