imx: clock: gate clk before changing pix clk mux

The LCDIF Pixel clock mux is not glitchless, so need
to gate before changing mux.

Also change enable_lcdif_clock prototype with a new input
parameter to indicate disable or enable.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/board/freescale/mx6sxsabresd/mx6sxsabresd.c b/board/freescale/mx6sxsabresd/mx6sxsabresd.c
index 965e511..0460cd9 100644
--- a/board/freescale/mx6sxsabresd/mx6sxsabresd.c
+++ b/board/freescale/mx6sxsabresd/mx6sxsabresd.c
@@ -504,7 +504,7 @@
 
 static int setup_lcd(void)
 {
-	enable_lcdif_clock(LCDIF1_BASE_ADDR);
+	enable_lcdif_clock(LCDIF1_BASE_ADDR, 1);
 
 	imx_iomux_v3_setup_multiple_pads(lcd_pads, ARRAY_SIZE(lcd_pads));