mb/*/*: Remove rtc nvram configurable baud rate

There have been discussions about removing this since it does not seem
to be used much and only creates troubles for boards without defaults,
not to mention that it was configurable on many boards that do not
even feature uart.

It is still possible to configure the baudrate through the Kconfig
option.

Change-Id: I71698d9b188eeac73670b18b757dff5fcea0df41
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/19682
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/include/console/uart.h

@@ -23,11 +23,6 @@
  * baudrate generator. */
 unsigned int uart_platform_refclk(void);
 
-/* Return the baudrate determined from option_table, or when that is
- * not used, CONFIG_TTYS0_BAUD.
- */
-unsigned int default_baudrate(void);
-
 /* Returns the divisor value for a given baudrate.
  * The formula to satisfy is:
  *    refclk / divisor = baudrate * oversample