This allows for early-printk to be specified (for existing UARTS at
least) without the need to edit Rules.mk.
The existing shortcuts are retained, but in a much more compact
fashion.
An unused EARLY_PRINTK_BAUD was removed from the zynqmq settings.
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: Julien Grall <julien.grall@linaro.org>