cfag12864bfb: Use sys_ instead of cfb_ framebuffer accessors

Because the framebuffer memory is allocated system RAM, use the sys_ drawing
libraries. It also fixes the following compile error:

  LD      .tmp_vmlinux1
drivers/built-in.o:(.data+0x8b48): undefined reference to `cfb_fillrect'
drivers/built-in.o:(.data+0x8b50): undefined reference to `cfb_copyarea'
drivers/built-in.o:(.data+0x8b58): undefined reference to `cfb_imageblit'

[adaplas]
Use fb_sys_read/write for the same reasons as above.

Signed-off-by: Avuton Olrich <avuton@gmail.com>
Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>