Correct /is4 encoding for EVEX instructions
Correct /is4 encoding for EVEX instructions

For EVEX instructions, /is4 can contain a fifth register bit, encoded
in bit 3 of the imm8.  Properly generate this case, and simplifiy the
/is4 generation code somewhat.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@linux.intel.com>

techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm,techkey/nasm