staging: sm7xxfb: usr fb_read and fb_write

Now since the Big-Endian and Little-Endian based calculations are moved
into a macro we can make fb_read() and fb_write() common for both
Little-Endian and Big-Endian.

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