userdebug版本开机串口log打开

在/bootable/bootloader/lk/app/mt_boot/mt_boot.c里修改：
if (!has_set_p2u) {
#ifdef USER_BUILD
sprintf(cmdline,"%s%s",cmdline," printk.disable_uart=1"); // printk.disable_uart=1 改为0
#else
sprintf(cmdline,"%s%s",cmdline," printk.disable_uart=0 ddebug_query=\"file *mediatek* +p ; file *gpu* =_\"");
#endif