It's common that UARTs are bound and probed before U-Boot relocation, in which case the clocks of UART and UART's pincontroller must be registered first. Let's apply DM_FLAG_PRE_RELOC to the driver, allowing it to bind before relocation. Signed-off-by: Yao Zi <ziyao@disroot.org> Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>