staging: sm7xxfb: use framebuffer_alloc and release

use the standard framebuffer_alloc() and framebuffer_release() instead
of custom defined function. for making that change we had to change a
member of the private structure from a variable to pointer and had to
touch almost all places of the file. since fb was changed into a pointer
so all instance of "sfb->fb." has been changed into "sfb->fb->".
now we will get build warning about smtc_alloc_fb_info() and
smtc_free_fb_info() to be unused which will be removed in the next
patch of the series.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>