fix(imx8m): make IMX_BOOT_UART_BASE autodetection option more obvious

Switch from IMX_BOOT_UART_BASE=0 to IMX_BOOT_UART_BASE=auto to make it
more obvious that the detection is based on the runtime autodetection.

In addition this moves the evaluation of IMX_BOOT_UART_BASE into the
makefile which removes the ugly conditional compilation as well.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Change-Id: I92c13607bf81c6267f4b6aee829d74902b7f72d2
6 files changed