riscv: tools: Prelink u-boot

Add prelink-riscv to arrange .rela.dyn and .rela.got
in compile time. So that u-boot can be directly
executed without fixup.

Signed-off-by: Chih-Mao Chen <cmchen@andestech.com>
Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Signed-off-by: Greentime Hu <green.hu@gmail.com>