ARM: imx6qdl: switch to use macro for clock ID

Instead of using enum for clock ID, let's switch imx6qdl clock driver to
use macro.  In this case, device tree can reuse these macros to improve
readability.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

diff --cc Documentation/devicetree/bindings/clock/imx6q-clock.txt
Simple merge

diff --cc arch/arm/mach-imx/clk-imx6q.c
Simple merge

diff --cc include/dt-bindings/clock/imx6qdl-clock.h
Simple merge