vfio-mdev: add missing MODULE_DESCRIPTION() macros

Since commit 1fffe7a3 ("script: modpost: emit a warning when the
description is missing"), a module without a MODULE_DESCRIPTION() will
result in a warning with make W=1. The following warnings are being
observed in samples/vfio-mdev:

WARNING: modpost: missing MODULE_DESCRIPTION() in samples/vfio-mdev/mtty.o
WARNING: modpost: missing MODULE_DESCRIPTION() in samples/vfio-mdev/mdpy.o
WARNING: modpost: missing MODULE_DESCRIPTION() in samples/vfio-mdev/mdpy-fb.o
WARNING: modpost: missing MODULE_DESCRIPTION() in samples/vfio-mdev/mbochs.o

Add the missing invocations of the MODULE_DESCRIPTION() macro to these
modules. And in the case of mtty.c, remove the now redundant instance
of the MODULE_INFO() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Link: https://lore.kernel.org/r/20240715-md-vfio-mdev-v2-1-59a4c5e924bc@quicinc.com


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>