riscv: tools: Fix prelink-riscv to work on big endian hosts

All ELF fields whose values are inspected by the code are converted to
CPU byteorder first.  Values which are copied verbatim (relocation
fixups) are not swapped to CPU byteorder and back as it is not needed.

Signed-off-by: Marcus Comstedt <marcus@mc.pp.se>
Cc: Rick Chen <rick@andestech.com>
Reviewed-by: Rick Chen <rick@andestech.com>