mtd-utils: Add configure switches to disable jffsX or ubifs tools

mtd-utils: Add configure switches to disable jffsX or ubifs tools

For some applications, like building a root filesystem for an embedded
device, it may be desireable to only build and install a subset of the
mtd-utils. This can be done throught the targets of the generated
Makefile and hand picking executables, however the jffsX and ubifs
utilities have external build dependencies that may not be needed.

This patch adds configure switches to disable building the jffsX and
ubifs utilities. Their respective build dependencies (zlib, lzo, uuid)
are only requested if the tools are being built.

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>
Reviewed-by: Richard Weinberger <richard@nod.at>