imx: mx6: Fix procedure to switch the parent of LDB_DI_CLK

imx: mx6: Fix procedure to switch the parent of LDB_DI_CLK

Due to incorrect placement of the clock gate cell in the ldb_di[x]_clk tree,
the glitchy parent mux of ldb_di[x]_clk can cause a glitch to enter the
ldb_di_ipu_div divider. If the divider gets locked up, no ldb_di[x]_clk is
generated, and the LVDS display will hang when the ipu_di_clk is sourced from
ldb_di_clk.

To fix the problem, both the new and current parent of the ldb_di_clk should
be disabled before the switch. This patch ensures that correct steps are
followed when ldb_di_clk parent is switched in the beginning of boot.

This patch was ported from the 3.10.17 NXP kernel
http://git.freescale.com/git/cgit.cgi/imx/linux-2.6-imx.git/commit/?h=imx_3.10.17_1.0.1_ga&id=eecbe9a52587cf9eec30132fb9b8a6761f3a1e6d

NXP errata number: ERR009219, EB821

Signed-off-by: Akshay Bhat <akshay.bhat@timesys.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>