target-mips: Fix the 64-bit case for microMIPS MOVE16 and MOVEP

target-mips: Fix the 64-bit case for microMIPS MOVE16 and MOVEP

Fix microMIPS MOVE16 and MOVEP instructions on 64-bit processors by
using register addition operations.

This copies the approach taken with MIPS16 MOVE instructions (I8_MOV32R
and I8_MOVR32 opcodes) and follows the observation that OPC_ADDU expands
to tcg_gen_mov_tl whenever `rt' is 0 and `rs' is not, therefore copying
`rs' to `rd' verbatim.  This is not the case with OPC_ADDIU where a
sign-extension from bit #31 is made, unless in the uninteresting case of
`rs' being 0, losing the upper 32 bits of the value copied for any
proper 64-bit values.

This also serves as an optimization as one op is produced in generated
code rather than two (again, unless `rs' is 0, where it doesn't change
anything).

Signed-off-by: Maciej W. Rozycki <macro@codesourcery.com>
Reviewed-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>