yaft: use the neutrino framebuffer functions to blit

* do not allocate a buffer but use the backbuffer of the neutrino fb
* use blit2FB to copy the terminal window onto the screen


Origin commit data
------------------
Commit: 5ba578c5dc
Author: Stefan Seyfried <seife@tuxbox-git.slipkontur.de>
Date: 2018-01-15 (Mon, 15 Jan 2018)

src/gui/widget/yaft/yaft_class.cpp

@@ -193,14 +193,12 @@ int YaFT::run(void)
 
 	/* normal exit */
 	term_die(&term);
-	fb_die(&fb);
 	return EXIT_SUCCESS;
 
 	/* error exit */
 tty_init_failed:
 	term_die(&term);
 term_init_failed:
-	fb_die(&fb);
 fb_init_failed:
 	return EXIT_FAILURE;
 }