driver/uart: Introduce a way for mainboard to override the baudrate

The rationale is to allow the mainboard to override the default
baudrate for instance by sampling GPIOs at boot.

A new configuration option is available for mainboards to select
this behaviour. It will then have to define the function
get_uart_baudrate to return the computed baudrate.

Change-Id: I970ee788bf90b9e1a8c6ccdc5eee8029d9af0ecc
Signed-off-by: Julien Viard de Galbert <jviarddegalbert@online.net>
Reviewed-on: https://review.coreboot.org/23713
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/cpu/allwinner/a10/uart.c

@@ -105,7 +105,7 @@ void uart_init(int idx)
 	struct a10_uart *uart_base = uart_platform_baseptr(idx);
 
 	/* Use default 8N1 encoding */
-	a10_uart_configure(uart_base, CONFIG_TTYS0_BAUD,
+	a10_uart_configure(uart_base, get_uart_baudrate(),
 		8, UART_PARITY_NONE, 1);
 	a10_uart_enable_fifos(uart_base);
 }

src/cpu/allwinner/a10/uart_console.c

@@ -44,7 +44,7 @@ void uart_fill_lb(void *data)
 	struct lb_serial serial;
 	serial.type = LB_SERIAL_TYPE_MEMORY_MAPPED;
 	serial.baseaddr = uart_platform_base(CONFIG_UART_FOR_CONSOLE);
-	serial.baud = CONFIG_TTYS0_BAUD;
+	serial.baud = get_uart_baudrate();
 	serial.regwidth = 1;
 	serial.input_hertz = uart_platform_refclk();
 	serial.uart_pci_addr = 0;

src/cpu/ti/am335x/uart.c

@@ -163,7 +163,7 @@ void uart_init(int idx)
 {
 	struct am335x_uart *uart = uart_platform_baseptr(idx);
 	uint16_t div = (uint16_t) uart_baudrate_divisor(
-		CONFIG_TTYS0_BAUD, uart_platform_refclk(), 16);
+		get_uart_baudrate(), uart_platform_refclk(), 16);
 	am335x_uart_init(uart, div);
 }
 
@@ -189,7 +189,7 @@ void uart_fill_lb(void *data)
 	struct lb_serial serial;
 	serial.type = LB_SERIAL_TYPE_MEMORY_MAPPED;
 	serial.baseaddr = uart_platform_base(CONFIG_UART_FOR_CONSOLE);
-	serial.baud = CONFIG_TTYS0_BAUD;
+	serial.baud = get_uart_baudrate();
 	serial.regwidth = 2;
 	lb_add_serial(&serial, data);