e-as (epiphany.cpu): mov rd,#imm16 discrepancy w/ isa documentation

32-bit `mov rd,#imm16`  

Bits 19:16 marked as dont-care in ISA documentation but explicitly set to 0x2 in epiphany.cpu

https://parallella.org/forums/viewtopic.php?f=23&t=3966

https://github.com/adapteva/epiphany-binutils-gdb/blob/epiphany-binutils-2.27/cpu/epiphany.cpu#L3056
```scheme
(+ OP4_IMM32 (f-opc-4-1 #x0) (f-opc-19-4 #x2) (f-dc-28-1 #x0) rd6 imm16)
```

