Enable LDB channel after display controller

FSL: ENGR00304402

In order to avoid any random pixelation issue, we should follow a correct
display controller/LDB initialization sequence, that is, LDB channel should
be enabled after its relevant display controller is enabled.  Since the
enable() callback of the mxc display driver is called after a display
controller is enabled, this patch uses the enable()/disable() callbacks
to replace the fb notifier callback implemented in the LDB driver.  Also,
we disable a LDB channel in the setup() callback of the mxc display driver
to make sure of the correct sequence in any fb set_par() function.  As the
enable()/disable() callbacks are always invoked with fb_blank(), this
patch drops the suspend()/resume() functions of the LDB driver which
do nothing but enable/disable LDB channels.  We also remove the code to
enable ldb di clocks because they can be enabled when their relevant
child pixel clocks are enabled.

Signed-off-by: Jeff Horn <jhorn@reachtech.com>