tcg/mips: fix invalid op definition errors

tcg/mips/tcg-target.h defines various operations conditionally depending
upon the isa revision, however these operations are included in
mips_op_defs[] unconditionally resulting in the following runtime errors
if CONFIG_DEBUG_TCG is defined:

Invalid op definition for movcond_i32
Invalid op definition for rotl_i32
Invalid op definition for rotr_i32
Invalid op definition for deposit_i32
Invalid op definition for bswap16_i32
Invalid op definition for bswap32_i32
tcg/tcg.c:1196: tcg fatal error

Fix with ifdefs like the i386 backend does for movcond_i32.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>