microblaze: Remove early printk setup

Early printk has been removed already that's why this setting doesn't make
any sense. Also change printk level from pr_info to pr_err.

Fixes: 96f0e6fc

 ("microblaze: remove redundant early_printk support")
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Stefan Asserhall <stefan.asserhall@xilinx.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>