[DM/FDT] Fix garble when booting

Fix garble caused by empty implementation of earlycon series
function in driver.If driver doesn't offer earlycon_id or rt_f
dt_earlycon_id.setup function but open option, the checking
of best_earlycon_id will failed.

Signed-off-by: 1078249029 <1078249029@qq.com>

components/drivers/ofw/fdt.c

@@ -23,7 +23,7 @@
 
 #include "ofw_internal.h"
 
-struct rt_fdt_earlycon fdt_earlycon rt_section(".bss.noclean.earlycon");
+struct rt_fdt_earlycon fdt_earlycon;
 
 RT_OFW_SYMBOL_TYPE_RANGE(earlycon, struct rt_fdt_earlycon_id, _earlycon_start = {}, _earlycon_end = {});