findMaskR11() was missing handling for duplex instructions. This caused
incorrect encoding when R_HEX_TPREL_11_X relocations were applied to
duplex instructions with large TLS offsets.
For duplex instructions, the immediate bits are located at positions
20-25 (mask 0x03f00000), not in the standard positions used for
non-duplex instructions.
This fix adds the isDuplex() check to findMaskR11() to return the
correct mask for duplex instruction encodings.
62d018b87a