greybus: switch to the term "manifest"

greybus: switch to the term "manifest"

We agreed to rename a few things to improve clarity.  This patch
implements one of those changes.  The blob of data that describes
what's relevant to Greybus within an Ara module will now be called
the "module manifest."  In addition, in the context of Greybus we'll
also be calling what's in an Ara module a "module" or "Greybus module."

So this patch renames some structures and updates some comments.  It
also renames "greybus_desc.h" to be "greybus_manifest.h", and renames
greybus_new_device() to be greybus_new_module().

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>