Revert "serial: 8250_mtk: Make sure to select the right FEATURE_SEL"

It was found that some MediaTek SoCs are incompatible with this
change. Also, this register was mistakenly understood as it was
related to the 16550A register layout selection but, at least
on some IPs, if not all, it's related to something else unknown.

This reverts commit 6f81fdde.
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Fixes: 6f81fdde ("serial: 8250_mtk: Make sure to select the right FEATURE_SEL")
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Link: https://lore.kernel.org/r/20220510122620.150342-1-angelogioacchino.delregno@collabora.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_mtk.c

@@ -54,9 +54,6 @@
 #define MTK_UART_TX_TRIGGER	1
 #define MTK_UART_RX_TRIGGER	MTK_UART_RX_SIZE
 
-#define MTK_UART_FEATURE_SEL	39	/* Feature Selection register */
-#define MTK_UART_FEAT_NEWRMAP	BIT(0)	/* Use new register map */
-
 #define MTK_UART_XON1		40	/* I/O: Xon character 1 */
 #define MTK_UART_XOFF1		42	/* I/O: Xoff character 1 */
 
@@ -575,10 +572,6 @@ static int mtk8250_probe(struct platform_device *pdev)
 		uart.dma = data->dma;
 #endif
 
-	/* Set AP UART new register map */
-	writel(MTK_UART_FEAT_NEWRMAP, uart.port.membase +
-	       (MTK_UART_FEATURE_SEL << uart.port.regshift));
-
 	/* Disable Rate Fix function */
 	writel(0x0, uart.port.membase +
 			(MTK_UART_RATE_FIX << uart.port.regshift));