added device support for 'rotate' and 'bgr'

This provides the basis for moving rotate and bgr from a driver argument to a device parameter.
added rotate and bgr arguments
added rotation support
fixes fbtft_set_addr_win() for values > 255. Thanks cnvogelg.
make it possible to disable tx buffer with txbuflen < -1
experimental 16-bit bus support
add buswidth=16 support
moved EXPORT_SYMBOL statements
add backlight support
HY28A support (partially)
hy28afb: slow down reading speed
hy28afb: fixed rotation and bgr
fbtft: add Start byte support
fbtft: add comment
fbtft: add fbtft_read_spi()
hy28afb: moved functionality to core
fbtft: added fbtft_write_gpio16_wr_latched()
fbtft: 16-bit latched write support
fbtft: fbtft_write_vmem16_bus16() no need for buffered write
fbtft: fbtft_write_vmem16_bus8() add Start byte support