Previously, fiptool only understood a fixed set of images as
specified in tbbr_config.c.  It preserved unknown images during
the update, unpack and remove operations but it was not possible to
explicitly refer to one of those unknown images.

Add a new --blob option to create/update/unpack/remove images that
are not known at compile time.  This is accomplished by specifying
the UUID and filename pair as shown below:

$ ./fiptool create --blob uuid=01234567-89ab-cdef-0123-456789abcdef,file=foo.bin fip.bin
$ ./fiptool info fip.bin
01234567-89ab-cdef-0123-456789abcdef: offset=0x60, size=0x1AA68

Fixes ARM-software/tf-issues#420

Change-Id: Iaac2504b9a4252289c09e73d29645cbe240f3a82
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>