fsl-diu-fb: remove check for pixel clock ranges

The Freescale DIU framebuffer driver defines two constants, MIN_PIX_CLK and
MAX_PIX_CLK, that are supposed to represent the lower and upper limits of
the pixel clock.  These values, however, are true only for one platform
clock rate (533MHz) and only for the MPC8610.  So the actual range for
the pixel clock is chip-specific, which means the current values are almost
always wrong.  The chance of an out-of-range pixel clock being used are also
remote.

Rather than try to detect an out-of-range clock in the DIU driver, we depend
on the board-specific pixel clock function (e.g. p1022ds_set_pixel_clock)
to clamp the pixel clock to a supported value.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>