MLK-12614 mxc IPUv3: common: Refactor pixel clock tree register implementation

MLK-12614 mxc IPUv3: common: Refactor pixel clock tree register implementation

This patch removes boilerplate code to register clocks for two DIs of one IPU.
Also, the char strings for storing the pixel clock parent names are wrongly
placed in the kernel rodata section, which will be overwritten when clocks
are registered.  This patch moves the problematic strings to stack.  Since
clk_register() will cache his own version from non-kernel-rodata space, this
may fix the issue.

Signed-off-by: Liu Ying <victor.liu@nxp.com>