fbdev: add drawing functions for framebuffers in system RAM

The generic drawing functions (cfbimgblt, cfbcopyarea, cfbfillrect) assume
that the framebuffer is in IO memory.  However, we have 3 drivers (hecubafb,
arcfb, and vfb) where the framebuffer is allocated from system RAM (via
vmalloc). Using _raw_read/write and family for these drivers (as used in
the cfb* functions) is illegal, especially in other platforms.

Create 3 new drawing functions, based almost entirely from the original
except that the framebuffer memory is assumed to be in system RAM.
These are named as sysimgblt, syscopyarea, and sysfillrect.

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>