staging: sm7xxfb: sm7xx becomes sm7xxfb

Rename sm7xx driver to sm7xxfb. Fix Kconfig and Makefile to fit the new
change.

Changes are coherent with the rest of stable framebuffer drivers. TODO
updated.

Signed-off-by: Javier M. Mellid <jmunhoz@igalia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>