Which exactly "UART RX" is in question?
What does it mean: "The driver is pl011"?
What does it mean: "My system keeps reboot"?
Please provide detailed technical description of the problem including the following attachments:
1) the processor connection schematics as searchable PDF
2) digital scope traces showing behaviour of the processor's reset signals corresponding to the QorIQ LS1021A Reference Manual, Figure 4-1. Power-on reset sequence