Enable iminfo command by default for all devices

Enable iminfo command by default for all devices

Since we support both types of image headers, we can enable
"iminfo" command by default for all devices.

Example output for image with custom TP-Link header:

uboot> imi 0x9F020000

Checking image at 0x9F020000...

   Vendor/image name:    TP-LINK Technologies ver. 1.0
   Firmware version:     3.16.9
   Hardware ID:          0x8410009
   Whole image size:     3.8 MB (3932160 bytes)
   Kernel size:          706.1 kB (723022 bytes)
   Rootfs size:          2.8 MB (2883584 bytes)
   Kernel load address:  0x80002000
   Kernel entry point:   0x801856F0

   Header CRC...  skipped
   Data CRC...    skipped

And for default U-Boot image header (Multi-File image here):

uboot> imi 0x9FE80000

Checking image at 0x9FE80000...

   Image name:    MIPS OpenWrt Linux-3.3.8
   Build date:    2015-10-22 03:41:11 UTC
   Architecture:  MIPS
   OS/image type: Linux Multi-File
   Compression:   LZMA
   Data size:     1 MB (1090582 bytes)
   Load address:  0x80060000
   Entry point:   0x80060000

   Multi-Image:
   > 1 MB (1090574 bytes)

   Header CRC...  OK!
   Data CRC...    OK!