tools: socfpgaimage: Print image header information

Print image header information if the header is verified.

Example output from mkimage "-l" option:

$ ./tools/mkimage -l spl/u-boot-spl.sfp
Image Type      : Cyclone V / Arria V SoC Image
Validation word : 0x31305341
Version         : 0x00000000
Flags           : 0x00000000
Program length  : 0x00003a59
Header checksum : 0x00000188

$ ./tools/mkimage -l spl/u-boot-spl.sfp
Image Type      : Arria 10 SoC Image
Validation word : 0x31305341
Version         : 0x00000001
Flags           : 0x00000000
Header length   : 0x00000014
Program length  : 0x000138e0
Program entry   : 0x00000014
Header checksum : 0x00000237

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>