efi_loader: new functions to print loaded image information

Introduce functions to print information about loaded images.

If we want to analyze an exception in an EFI image we need the offset
between the PC and the start of the loaded image.

With efi_print_image_info() we can print the necessary information for a
single image, e.g.

UEFI image [0xbffe6000:0xbffe631f] pc=0x138 '/\snp.efi'

efi_print_image_infos() provides output for all loaded images.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>