xenctx: Add 16 bit output

xenctx: Add 16 bit output

This output happens on !guest_protected_mode.  The cpu is in 16 bit
mode in this case.

For example:

$ xenctx 4
cs:eip: f000:0000d61b
flags: 00000002 nz
ss:esp: 0000:00001fee
eax: 0000ffc2   ebx: 00000049   ecx: 00000049   edx: ffffffff
esi: 00000000   edi: 00000010   ebp: 00001ff0
 ds:     e000    es:     0040    fs:     0000    gs:     0000
Code (instr addr 000fd61b)
04 67 66 8b 70 08 67 66 8b 68 0c 67 66 8b 58 10 67 66 8b 50 14 <67> 66 8b 48 18 67 8e 40 02 67 ff

Stack:
 8e30 0000 0246 812f 0000 0206 80e7 0080 0080

$ xenctx 4 -d 0x00001fee -m 0x00001fee -l 1
Memory (address 1fee):
 8e30 0000 0246 812f 0000 0206 80e7 0080 0080 c2c2 c2c2 c2c2 c2c2 c2c2 c2c2 c2c2

Stack:
 8e30 0000 0246 812f 0000 0206 80e7 0080 0080

Signed-off-by: Don Slutz <dslutz@verizon.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>